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1

Onset conditions for gas phase reaction and nucleation in the CVD of transition metal oxides  

NASA Technical Reports Server (NTRS)

A combined experimental/theoretical study is presented of the onset conditions for gas phase reaction and particle nucleation in hot substrate/cold gas CVD of transition metal oxides. Homogeneous reaction onset conditions are predicted using a simple high activation energy reacting gas film theory. Experimental tests of the basic theory are underway using an axisymmetric impinging jet CVD reactor. No vapor phase ignition has yet been observed in the TiCl4/O2 system under accessible operating conditions (below substrate temperature Tw = 1700 K). The goal of this research is to provide CVD reactor design and operation guidelines for achieving acceptable deposit microstructures at the maximum deposition rate while simultaneously avoiding homogeneous reaction/nucleation and diffusional limitations.

Collins, J.; Rosner, D. E.; Castillo, J.

1992-01-01

2

Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania  

NASA Technical Reports Server (NTRS)

We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

1994-01-01

3

Numerical analysis of an impinging jet reactor for the CVD and gas-phase nucleation of titania  

NASA Astrophysics Data System (ADS)

We model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (approximately 11 percent at 1000 K), the reduction rates due to Soret transport is substantial (approximately 75 percent at 1000 K).

Gokoglu, Suleyman A.; Stewart, Gregory D.; Collins, Joshua; Rosner, Daniel E.

1994-06-01

4

Influence of quantity and energy of the particles in gas phase on nucleation of the HFCVD of diamond films  

Microsoft Academic Search

In this paper, the nucleation of diamond films was studied with the varied bias value and mass current density by adjusting the gas flow rate through the chamber. Results showed that the two parameters above greatly influenced the nucleation density and the morphology of diamond films. Both bias value and mass current density had an optimum value in which the

G. H. Song; C. Sun; B. Wang; A. Y. Wang; R. F. Huang; L. S. Wen

2001-01-01

5

Nucleation, growth and transformation of amorphous and crystalline solids condensing from the gas phase  

NASA Astrophysics Data System (ADS)

The condensation of solids was investigated from the initial stage through continuous film growth, using evaporation and high-energy ion-beam sputtering. Consideration is given to germanium condensing on a variety of amorphous and crystalline substrates. Nucleation parameters, such as the activation energies of surface diffusion and adsorption and the critical nucleus size, were determined using an atomistic model for nucleation. Two flux and temperature dependent structural-order transitions were observed in the initial nucleation stages and found to coincide with corresponding transitions in the critical nucleus size. Correlation was also established between these transitions and two structural transitions occurring during continuous film growth. All results were distinctly affected by the vapor state of the adsorbates, implying considerable correlation between condensation on solid surfaces and in a vapor.

Krikorian, E.; Sneed, R. J.

1979-09-01

6

Pore-scale interfacial dynamics during gas-supersaturated water injection in porous media - on nucleation, growth and advection of disconnected fluid phases (Invited)  

NASA Astrophysics Data System (ADS)

Degassing and in situ development of a mobile gas bubbles occur when injecting supersaturated aqueous phase into water-saturated porous media. Supersaturated water injection (SWI) has potentially significant applications in remediation of soils contaminated by non-aqueous phase liquids and in enhanced oil recovery. Pore network simulations indicate the formation of a region near the injection boundary where gas phase nuclei are activated and grow by mass transfer from the flowing supersaturated aqueous phase. Ramified clusters of gas-filled pores develop which, owing to the low prevailing Bond number, grow laterally to a significant extent prior to the onset of mobilization, and are thus likely to coalesce. Gas cluster mobilization invariably results in fragmentation and stranding, such that a macroscopic region containing few tenuously connected large gas clusters is established. Beyond this region, gas phase nucleation and mass transfer from the aqueous phase are limited by diminishing supply of dissolved gas. New insights into SWI dynamics are obtained using rapid micro-visualization in transparent glass micromodels. Using high-speed imaging, we observe the nucleation, initial growth and subsequent fate (mobilization, fragmentation, collision, coalescence and stranding) of CO2 bubbles and clusters of gas-filled pores and analyze cluster population statistics. We find significant support for the development of invasion-percolation-like patterns, but also report on hitherto unaccounted for gas bubble behavior. Additionally, we report for the first time on the acoustic emission signature of SWI in porous media and relate it to the dynamics of bubble nucleation and growth. Finally, we identify the pore-scale mechanisms associated with the mobilization and subsequent recovery of a residual non-aqueous phase liquid due to gas bubble dynamics during SWI.

Or, D.; Ioannidis, M.

2010-12-01

7

Formation of Protein Condensed Phases: Nucleation Mechanisms.  

PubMed

Proteins in solution form a number of condensed phases. Even omitting the amyloid structures formed after partial protein unfolding, these phases include crystals, polymers, and other solid aggregates, as well as dense liquids and gels. Some of these condensed phases underlie pathological conditions, others play a crucial role in the biological function of the respective protein or are an essential part of its laboratory or industrial processing. In this review, we summarize the fundamentals and recent findings on the kinetics of nucleation of dense liquid droplets and crystals. We define the transition from nucleation to spinodal decomposition for these two phase transitions. We review the two-step mechanism of protein crystal nucleation, in which mesoscopic metastable protein clusters serve as precursors to the ordered crystal nuclei. The concepts and mechanisms reviewed here provide powerful tools for control of the nucleation process by varying the solution thermodynamic parameters. PMID:22489787

Vekilov, Peter G

2012-04-01

8

Nucleation and growth of metastable phases in thin films  

NASA Astrophysics Data System (ADS)

This research focuses on the synthesis of metastable phases in thin films away from their thermal equilibrium conditions. The goal of this study is not only to achieve the desirable metastable phases, but also to understand their nucleation and growth process, so that the principles employed in this study may be applied to other material systems. Several material systems have been used, including aluminum nitride, aluminum oxide, boron nitride and diamond. Different factors, which affect the formation of the metastable phases, have been studied. The first three materials, AlN, Al2O3 and BN were deposited using magnetron sputter techniques, while diamond was grown by direct ion-beam deposition. The metastable phases can be obtained by different routes. Bl-AlN was stabilized in epitaxial AlN/VN (001) superlattices with an AlN layer thickness less than 4.0 nm, a so-called epitaxial stabilization effect, taking advantage of the material system itself---stabilizing the metastable phase based on the small interfacial energy between Bl-AlN and VN. Another method to achieve metastable phases in thin films is to modify the conventional deposition techniques, i.e., increasing the ion-bombardment of the growing films. Crystalline alumina was obtained using an intensified ionized magnetron sputtering, where an increased ion-flux to the substrate was obtained using a magnetic trap generated by an external solenoid. Cubic boron nitride (cBN) was synthesized using a similar method, i.e. ion-bombardment assisted magnetron sputtering. Factors affecting the cubic phase formation were investigated, including pre deposition vacuum, film stoichiometry, deposition temperature, and substrate bias. Study of the micro-environments of tBN prior to the cBN nucleation disclosed different types of cBN nucleation and growth associated with different film internal stress levels. In order to precisely control the ion-bombardment during film deposition, direct ion-beam deposition was employed to study diamond nucleation on silicon. Ion beam nucleation of diamond using different reactive gas ratios leads to different nuclei qualities, which may be explained by the ion solid interaction and the effect of several competing nucleation mechanisms.

Li, Quan

9

Nucleation and growth of Nb nanoclusters during plasma gas condensation  

SciTech Connect

Niobium nanoclusters were produced using a plasma gas condensation process. The influence of gas flow rate, aggregation length, and source current on the nanocluster nucleation and growth were analyzed. Nanoclusters with an average diameter from 4 nm to 10 nm were produced. Cluster size and concentration were tuned by controlling the process inputs. The effects of each parameter on the nucleation zone, growth length, and residence time was examined. The parameters do not affect the cluster formation and growth independently; their influence on cluster formation can be either cumulative or competing. Examining the nucleation and growth over a wide combination of parameters provided insight into their interactions and the impact on the growth process. These results provide the opportunity for a broader understanding into the nucleation and growth of nanoclusters and some insights into how process parameters interact during deposition. This knowledge will enhance the ability to create nanoclusters with desired size dispersions.

Bray, K. R.; Jiao, C. Q. [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States)] [UES, Inc., 4401 Dayton-Xenia Rd, Dayton, Ohio 45432 (United States); DeCerbo, J. N. [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)] [Air Force Research Laboratory, AFRL/RQQE, 1950 Fifth St., WPAFB, Ohio 45433 (United States)

2013-06-21

10

Kinetics of gas bubble nucleation and growth in magmatic melt at its rapid decompression  

NASA Astrophysics Data System (ADS)

The model of gas bubble growth in high-viscous gas-saturated magmatic melt, subjected to rapid decompression, is presented in the current study. It is shown that consideration of unsteady character of the process is extremely important in a wide range of supersaturation. The analytical solution is found for the profile of dissolved gas concentration and the rate of bubble growth. The model of kinetics of overall degassing is developed. This model is based on distinguishing the so-called "forbidden" zone in the melt volume with suppressed formation of the new nucleation sites. The simple analytical dependences of the number of nucleating bubbles and typical nucleation time on the value of initial decompression were derived together with time dependence of volumetric concentration of the gas phase. Our results match the available experimental data.

Chernov, A. A.; Kedrinsky, V. K.; Pil'nik, A. A.

2014-11-01

11

Phase Field Theory of Nucleation and Polycrystalline Pattern Formation  

E-print Network

We review our recent modeling of crystal nucleation and polycrystalline growth using a phase field theory. First, we consider the applicability of phase field theory for describing crystal nucleation in a model hard sphere fluid. It is shown that the phase field theory accurately predicts the nucleation barrier height for this liquid when the model parameters are fixed by independent molecular dynamics calculations. We then address various aspects of polycrystalline solidification and associated crystal pattern formation at relatively long timescales. This late stage growth regime, which is not accessible by molecular dynamics, involves nucleation at the growth front to create new crystal grains in addition to the effects of primary nucleation. Finally, we consider the limit of extreme polycrystalline growth, where the disordering effect due to prolific grain formation leads to isotropic growth patterns at long times, i.e., spherulite formation. Our model of spherulite growth exhibits branching at fixed grain misorientations, induced by the inclusion of a metastable minimum in the orientational free energy. It is demonstrated that a broad variety of spherulitic patterns can be recovered by changing only a few model parameters.

L. Granasy; T. Pusztai; T. Borzsonyi

2007-03-26

12

Nucleation and Bulk Crystallization in Binary Phase Field Theory  

E-print Network

We present a phase field theory for binary crystal nucleation. In the one-component limit, quantitative agreement is achieved with computer simulations (Lennard-Jones system) and experiments (ice-water system) using model parameters evaluated from the free energy and thickness of the interface. The critical undercoolings predicted for Cu-Ni alloys accord with the measurements, and indicate homogeneous nucleation. The Kolmogorov exponents deduced for dendritic solidification and for "soft-impingement" of particles via diffusion fields are consistent with experiment.

Laszlo Granasy; Tamas Borzsonyi; Tamas Pusztai

2002-04-05

13

Inhomogeneous nucleation in a quark-hadron phase transition  

NASA Astrophysics Data System (ADS)

The effect of subcritical hadron bubbles on a first-order quark-hadron phase transition is studied. These subcritical hadron bubbles are created due to thermal fluctuations, and can introduce a finite amount of phase mixing (quark phase mixed with hadron phase) even at and above the critical temperature. For reasonable choices of surface tension and correlation length, as obtained from the lattice QCD calculations, we show that the amount of phase mixing at the critical temperature remains below the percolation threshold. Thus, as the system cools below the critical temperature, the transition proceeds through the nucleation of critical-size hadron bubbles from a metastable quark-gluon phase (QGP), within an inhomogeneous background populated by an equilibrium distribution of subcritical hadron bubbles. The inhomogeneity of the medium results in a substantial reduction of the nucleation barrier for critical bubbles. Using the corrected nucleation barrier, we estimate the amount of supercooling for different parameters controlling the phase transition, and briefly discuss its implications to cosmology and heavy-ion collisions.

Shukla, P.; Mohanty, A. K.; Gupta, S. K.; Gleiser, Marcelo

2000-11-01

14

Quantum Nucleation of Phase Slips in 1-d Superfluids  

NASA Astrophysics Data System (ADS)

The rate for quantum nucleation of phase slips past an impurity in a one-dimensional superfluid is computed. Real time evolution of the nonlinear Schrödinger equation shows that there is a critical velocity vc below which solutions are time-independent [1,2]; this is the regime of quantum phase slip nucleation. We start with the Gross-Pitaevskii model in the presence of an impurity potential, and derive the Euclidean action for a space-time vortex-antivortex pair, which describes a phase slip event. The action is computed as a function of the superfluid velocity v and the impurity potential width and depth.l [1] V. Hakim, Phys. Rev. E 55, 2835 (1997).l [1] J. A. Freire, D. P. Arovas, and H. Levine, Phys. Rev. Lett (in press, 1997).l

Arovas, Daniel

1998-03-01

15

Nucleation of the diamond phase in aluminium-solid solutions  

NASA Technical Reports Server (NTRS)

Precipitation was studied from fcc solid solutions with silicon, germanium, copper and magnesium. Of all these elements only silicon and germanium form diamond cubic (DC) precipitates in fcc Al. Nucleation of the DC structure is enhanced if both types of atom are dissolved in the fcc lattice. This is interpreted as due to atomic size effects in the prenucleation stage. There are two modes of interference of fourth elements with nucleation of the DC phase in Al + Si, Ge. The formation of the DC phase is hardly affected if the atoms (for example, copper) are rejected from the (Si, Ge)-rich clusters. If additional types of atom are attracted by silicon and/or germanium, DC nuclei are replaced by intermetallic compounds (for example Mg2Si).

Hornbogen, E.; Mukhopadhyay, A. K.; Starke, E. A., Jr.

1993-01-01

16

Observing classical nucleation theory at work by monitoring phase transitions with molecular precision  

PubMed Central

It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned. PMID:25465441

Sleutel, Mike; Lutsko, Jim; Van Driessche, Alexander E.S.; Durán-Olivencia, Miguel A.; Maes, Dominique

2014-01-01

17

Observing classical nucleation theory at work by monitoring phase transitions with molecular precision  

NASA Astrophysics Data System (ADS)

It is widely accepted that many phase transitions do not follow nucleation pathways as envisaged by the classical nucleation theory. Many substances can traverse intermediate states before arriving at the stable phase. The apparent ubiquity of multi-step nucleation has made the inverse question relevant: does multistep nucleation always dominate single-step pathways? Here we provide an explicit example of the classical nucleation mechanism for a system known to exhibit the characteristics of multi-step nucleation. Molecular resolution atomic force microscopy imaging of the two-dimensional nucleation of the protein glucose isomerase demonstrates that the interior of subcritical clusters is in the same state as the crystalline bulk phase. Our data show that despite having all the characteristics typically associated with rich phase behaviour, glucose isomerase 2D crystals are formed classically. These observations illustrate the resurfacing importance of the classical nucleation theory by re-validating some of the key assumptions that have been recently questioned.

Sleutel, Mike; Lutsko, Jim; van Driessche, Alexander E. S.; Durán-Olivencia, Miguel A.; Maes, Dominique

2014-12-01

18

Electromagnetic emissions during seismic nucleation phase of stick-slips  

NASA Astrophysics Data System (ADS)

I. Introduction The size of seismic nucleation is determined by the characteristic wavelength of slip surface topography, and some scaling laws are derived from it (Ohnaka and Shen, 1999). Alternative characteristic wavelength should be introduced for natural faults because they are associated with layers of fault gouge. Riedel shear will be an equivalent since it is a characteristic structure inside fault zones. II. Method of stick- slip experiments Experimental apparatus: tri-axial apparatus. Samples: granite and gabbro cylinders of 20mmx40mm. Precut surface: 50 degree against sample axis and mirror-finished. Simulated fault gouge: quartz and gabbro powder of 0.25g. Sensors: strain gauges for measurements of axial stress and slip distance as well as three shear strain gauges pasted along a slip surface, three pairs of electrodes for measurement of triboelectric potentials. Data acquisition: continuously and synchronously at 2MHz. Experimental procedure: loading of axial stress after holding at confining pressure of 80-180 MPa and shear stress at 250 MPa during 0.1-1 hour for compaction of gouge. III. Experimental results 1) Stick-slips on bare surfaces Fluctuations of the electrode potentials during main stick-slip events are 55-180mV. Gabbro and granite samples do not show significant differences in magnitude of electrode potential. Any experimental runs were not associated with nucleation phases. Prior to main stick-slip events spike-like signals of electrode potentials were sometimes found synchronously with very small stress drops less than 1MPa. The amplitudes are less than 30mV, and they decayed exponentially. 2) Stick-slips with fault gouge Stress drops and fluctuations of electrode potentials at main stick-slip events are 7-400 MPa, 17-200mV+. Significant differences in fluctuations of electrode potentials were not found between granite and gabbro samples. About 30% of all experimental runs were associated with a nucleation phase. Slip distance, stress drop, duration and the maximum fluctuation of electrode potentials were 0.02mm, 14MPa, 0.3sec and 20mV in an experimental run, and the latter three were 3.5MPa, 0.35sec and 4mV in another run. Three pairs of strain gauges recorded the initial site and its propagation of a seismic nucleation. The potentials of three pairs of electrodes also fluctuated synchronously. The pulse-like electrode signals were sometimes found also for these experiments. IV. Discussions and conclusions 1) The reason why the stick-slips on bare surfaces were not associated with a nucleation phase is attributed to mirror-finished smooth and flat precut surfaces. 2) Irrespective of granite or gabbro powders of fault gouge, there were not significant differences in magnitude of pulse-like fluctuations of electrode potentials. This is the case for main stick-slip events. These indicate that the causes of the electric signals are not piezoelectric effect but triboelectricity and/or fracto-emission. 3) Since the fluctuations of electrode potentials are synchronous with the initiation and propagation of a nucleation, the former is attributed to the latter. 4) It is very likely that nucleation is quasi-static slip on a Riedel shear because the length of a nuclei estimated from slip during nucleation phases is the same order as the length of Riedel shears.

Onuma, K.; Otsuki, K.

2008-12-01

19

Homogeneous nucleation of particles from the vapor phase in thermal plasma synthesis  

Microsoft Academic Search

Particle nucleation and growth are simulated for iron vapor in a thermal plasma reactor with an assumed one-dimensional flow field and decoupled chemistry and aerosol dynamics. Including both evaporation and coagulation terms in the set of cluster-balance rate equations, a sharply defined homogeneous nucleation event is calculated. Following nucleation the vapor phase is rapidly depleted by condensation, and thereafter particle

S. L. Girshick; C.-P. Chiu

1989-01-01

20

Experimental studies of the vapor phase nucleation of refractory compounds. VI. The condensation of sodium.  

PubMed

In this paper we discuss the condensation of sodium vapor and the formation of a sodium aerosol as it occurs in a gas evaporation condensation chamber. A one-dimensional model describing the vapor transport to the vapor/aerosol interface was employed to determine the onset supersaturation, in which we assume the observed location of the interface is coincident with a nucleation rate maximum. We then present and discuss the resulting nucleation onset supersaturation data within the context of nucleation theory based on the liquid droplet model. Nucleation results appear to be consistent with a cesium vapor-to-liquid nucleation study performed in a thermal diffusion cloud chamber. PMID:16108655

Martínez, Daniel M; Ferguson, Frank T; Heist, Richard H; Nuth, Joseph A

2005-08-01

21

Nucleation in the atmosphere  

NASA Astrophysics Data System (ADS)

Small particles play major roles in modulating radiative and hydrological fluxes in the atmosphere and thus they impact both climate (IPCC 2007) and weather. Most atmospheric particles outside clouds are created in situ through nucleation from gas phase precursors and most ice particles within clouds are formed by nucleation, usually from the liquid. Thus, the nucleation process is of great significance in the Earth's atmosphere. The theoretical examination of nucleation in the atmosphere has been based mostly on classical nucleation theory. While diagnostically very useful, the prognostic skill demonstrated by this approach has been marginal. Microscopic approaches such as molecular dynamics and density functional theory have also proven useful in elucidating various aspects of the process but are not yet sufficiently refined to offer a significant prognostic advantage to the classical approach, due primarily to the heteromolecular nature of atmospheric nucleation. An important aspect of the nucleation process in the atmosphere is that the degree of metastability of the parent phase for the nucleation is modulated by a number of atmospheric processes such as condensation onto pre-existing particles, updraft velocities that are the main driving force for supersaturation of water (a major factor in all atmospheric nucleation), and photochemical production rates of nucleation precursors. Hence, atmospheric nucleation is both temporally and spatially inhomogeneous.

Hegg, D. A.; Baker, M. B.

2009-05-01

22

Monte Carlo tests of nucleation concepts in the lattice gas model.  

PubMed

The conventional theory of homogeneous and heterogeneous nucleation in a supersaturated vapor is tested by Monte Carlo simulations of the lattice gas (Ising) model with nearest-neighbor attractive interactions on the simple cubic lattice. The theory considers the nucleation process as a slow (quasistatic) cluster (droplet) growth over a free energy barrier ?F(*), constructed in terms of a balance of surface and bulk term of a critical droplet of radius R(*), implying that the rates of droplet growth and shrinking essentially balance each other for droplet radius R=R(*). For heterogeneous nucleation at surfaces, the barrier is reduced by a factor depending on the contact angle. Using the definition of physical clusters based on the Fortuin-Kasteleyn mapping, the time dependence of the cluster size distribution is studied for quenching experiments in the kinetic Ising model and the cluster size ?(*) where the cluster growth rate changes sign is estimated. These studies of nucleation kinetics are compared to studies where the relation between cluster size and supersaturation is estimated from equilibrium simulations of phase coexistence between droplet and vapor in the canonical ensemble. The chemical potential is estimated from a lattice version of the Widom particle insertion method. For large droplets it is shown that the physical clusters have a volume consistent with the estimates from the lever rule. Geometrical clusters (defined such that each site belonging to the cluster is occupied and has at least one occupied neighbor site) yield valid results only for temperatures less than 60% of the critical temperature, where the cluster shape is nonspherical. We show how the chemical potential can be used to numerically estimate ?F(*) also for nonspherical cluster shapes. PMID:23767652

Schmitz, Fabian; Virnau, Peter; Binder, Kurt

2013-05-01

23

Gas Phase Nanoparticle Synthesis  

NASA Astrophysics Data System (ADS)

This book deals with gas-phase nanoparticle synthesis and is intended for researchers and research students in nanomaterials science and engineering, condensed matter physics and chemistry, and aerosol science. Gas-phase nanoparticle synthesis is instrumental to nanotechnology - a field in current focus that raises hopes for environmentally benign, resource-lean manufacturing. Nanoparticles can be produced by many physical, chemical, and even biological routes. Gas-phase synthesis is particularly interesting since one can achieve accurate manufacturing control and hence industrial viability.

Granqvist, Claes; Kish, Laszlo; Marlow, William

24

Nucleation, kinetics and morphology of displacive phase transformations in iron  

NASA Astrophysics Data System (ADS)

An extensive, systematic molecular dynamics (MD) study is performed for analysing the nucleation, kinetics and morphology characteristics of thermally-induced, displacive phase transformations from face-centred cubic (fcc) to body-centred cubic (bcc) iron. At the atomic level these transformation characteristics are influenced by a number of factors, including (i) the appearance of free surfaces, (ii) the initial presence of fcc-bcc grain boundaries, (iii) the existence of point defects (i.e., atomic vacancies) near a grain boundary, (iv) the initial thermal velocities of the atoms, and (v) the specific interatomic potential used. Other MD studies that capture the overall transformation behaviour of iron well have often underestimated or ignored the influence by these factors on the transformation response, with the risk of putting the accuracy, generality and physical explanation of the MD results on loose grounds. The present research illustrates the relative contribution of each of the above factors by means of a detailed comparison study for three different interatomic potentials. The accuracy of the interatomic potentials is established by validating for the fcc and bcc phases the calculated elastic moduli, cohesive energy, vacancy formation energy and interfacial energy against experimental and ab initio data reported in the literature. The importance of calibrating material data of both the stable bcc phase and the metastable fcc phase - instead of the stable bcc phase only - is demonstrated. The numerical results call for general caution when interpreting phenomena that start close to instability points and therefore are sensitive to small disturbances; a large spread in the overall transformation time is found under different initial thermal velocities, interfacial lattice incoherence, boundary conditions (free vs. periodic), and interatomic potentials, where for completely transformed atomic systems the discrepancy between the maximum and minimum transformation time appears to be more than a factor of 150. The transformation time is phenomenologically related to the overall activation energy and the cohesive energy difference of the fcc and bcc phases, which, beyond a certain combination of values, may even prevent the transformation process from occurring. Also, the morphology of the bcc product phase is remarkably sensitive to the type of boundary conditions and the choice of interatomic potential, while the influence by both the set of initial thermal velocities and the interfacial lattice incoherence only becomes apparent for specific atomic samples that transform relatively slowly. The presence of fcc-bcc grain boundaries increases the spatial heterogeneity of transformation events, with the appearance of an increasing number of vacancies at the grain boundary giving rise to a larger overall transformation time. The 10 main results following from the present MD study are conveniently summarised at the end of this communication.

Suiker, A. S. J.; Thijsse, B. J.

2013-11-01

25

Electron diffraction data on nucleation and growth of an hcp phase in homogeneous (Ar) and heterogeneous (Ar-Kr) clusters  

NASA Astrophysics Data System (ADS)

The nucleation and growth of the hcp phase in homogeneous (Ar) and heterogeneous (Ar-Kr) clusters formed in adiabatically expanding supersonic jets of the inert gases are studied by electron diffraction. The average size of the clusters ranges from 2 × 103 to 1 × 105 atoms/cluster. A threshold size of the clusters is found at which an hcp phase forms along with the fcc structure. The relative amount of the hcp phase in the single crystal clusters increases with their size. The relative volume of the hcp phase in the heterogeneous clusters exceeds that in homogeneous clusters of the same size. A correlation is established between the relative volume of the hcp phase in the clusters and the number of "defect" planes contained in the fcc matrix from which hcp phase nucleates. It is found that in very large (? ? 150 Å) polycrystalline aggregations the fraction of the hcp phase reaches a maximum and does not increase as the clusters become larger. A mechanism is proposed for the nucleation and growth of the hcp phase in inert gas clusters.

Danylchenko, O. G.; Kovalenko, S. I.; Konotop, O. P.; Samovarov, V. N.

2014-12-01

26

Void Nucleation and Growth in Dual-Phase Steel 600 during Uniaxial Tensile Testing  

NASA Astrophysics Data System (ADS)

Commercial dual-phase (DP) steel in sheet form and comprised of ferrite, martensite, and bainite was subjected to uniaxial tension up to fracture. The damage characteristics were studied through extensive quantitative metallography and scanning electron microscope (SEM) observations of polished sections and fracture surfaces of failed specimens. The observed void nucleation mechanisms include nucleation at the martensite/ferrite interface or triple junction (most predominant), nucleation due to the cracking of martensite particles, and nucleation at the inclusions. The void characteristics in terms of area fraction, void density, void size ranges, and void orientations were analyzed as a function of thickness strain from various regions of the different uniaxial tensile test specimens taken to fracture. The damage analysis suggests that the void nucleation occurs during the entire deformation process with an almost constant rate and this rate reduces before fracture. A nucleation strain of 0.15 has been estimated for this material.

Avramovic-Cingara, G.; Saleh, Ch. A. R.; Jain, M. K.; Wilkinson, D. S.

2009-12-01

27

Fluid phase thermodynamics : I) nucleate pool boiling of oxygen under magnetically enhanced gravity and II) superconducting cavity resonators for high-stability frequency references and precision density measurements of helium-4 gas  

NASA Astrophysics Data System (ADS)

Although fluids are typically the first systems studied in undergraduate thermodynamics classes, we still have only a rudimentary phenomenological understanding of these systems outside of the classical and equilibrium regimes. Two experiments will be presented. First, we present progress on precise measurements of helium-4 gas at low temperatures (1 K-5 K). We study helium because at low densities it is an approximately ideal gas but at high densities the thermodynamic properties can be predicted by numerical solutions of Schroedinger's equation. By utilizing the high resolution and stability in frequency of a superconducting microwave cavity resonator we can measure the dielectric constant of helium-4 to parts in 109, corresponding to an equivalent resolution in density. These data will be used to calculate the virial coefficients of the helium gas so that we may compare with numerical predictions from the literature. Additionally, our data may allow us to measure Boltzmann's constant to parts in 108, a factor of 100 improvement over previous measurements. This work contains a description of the nearly-completed apparatus and the methods of operation and data analysis for this experiment. Data will be taken by future researchers.The second experiment discussed is a study of nucleate pool boiling. To date, no adequate quantitative model exists of this everyday phenomenon. In our experiment, we vary one parameter inaccessible to most researchers, gravity, by applying a magnetic force to our test fluid, oxygen. Using this technique, we may apply effective gravities of 0-80 times Earth's gravitational acceleration (g). In this work we present heat transfer data for the boiling of oxygen at one atmosphere ambient pressure for effective gravity values between 1g and 16g . Our data describe two relationships between applied heat flux and temperature differential: at low heat flux the system obeys a power law and at high heat flux the behavior is linear. We find that the transition heat flux between these two regimes scales as the 4th root of the gravitational acceleration, which may indicate a relationship to the critical heat flux. Additionally, we find that the low heat flux power law exponent is independent of gravity and the power law scale coefficient increases linearly with gravity.

Corcovilos, Theodore Allen

28

Nonequilibrium thermodynamics of nucleation  

NASA Astrophysics Data System (ADS)

We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects.

Schweizer, M.; Sagis, L. M. C.

2014-12-01

29

Exploring the discrepancies between experiment, theory, and simulation for the homogeneous gas-to-liquid nucleation of 1-pentanol  

NASA Astrophysics Data System (ADS)

Using an efficient Monte Carlo approach known as Aggregation-Volume-bias Monte Carlo with self-adaptive Umbrella Sampling and Histogram Reweighting (AVUS-HR), we obtained the nucleation free energy profile of 1-pentanol at various temperatures from 220 to 360 K. From these profiles, differences between the free energy barrier heights obtained from our simulations and those predicted by the classical nucleation theory (CNT) were calculated. Our results strongly support that the logarithm of the nucleation rate ratio between simulation (or experiment) and CNT increases almost linearly with the inverse temperature. Among the various factors that contribute to the discrepancy between simulation and CNT nucleation rates, the nonzero surface free energy of the monomer included in the CNT makes the largest contribution. On the molecular level, the simulations indicate that a gas-phase cluster of 1-pentanol molecules is relatively compact and can contain multiple hydrogen bonded aggregates of various sizes and that this aggregate size distribution depends strongly on temperature and also on the overall size of the cluster system.

Nellas, Ricky B.; Keasler, Samuel J.; Siepmann, J. Ilja; Chen, Bin

2010-04-01

30

Nucleation of ordered solid phases of proteins via a disordered high-density state: Phenomenological approach  

NASA Astrophysics Data System (ADS)

Nucleation of ordered solid phases of proteins triggers numerous phenomena in laboratory, industry, and in healthy and sick organisms. Recent simulations and experiments with protein crystals suggest that the formation of an ordered crystalline nucleus is preceded by a disordered high-density cluster, akin to a droplet of high-density liquid that has been observed with some proteins; this mechanism allowed a qualitative explanation of recorded complex nucleation kinetics curves. Here, we present a simple phenomenological theory that takes into account intermediate high-density metastable states in the nucleation process. Nucleation rate data at varying temperature and protein concentration are reproduced with high fidelity using literature values of the thermodynamic and kinetic parameters of the system. Our calculations show that the growth rate of the near-critical and supercritical ordered clusters within the dense intermediate is a major factor for the overall nucleation rate. This highlights the role of viscosity within the dense intermediate for the formation of the ordered nucleus. The model provides an understanding of the action of additives that delay or accelerate nucleation and presents a framework within which the nucleation of other ordered protein solid phases, e.g., the sickle cell hemoglobin polymers, can be analyzed.

Pan, Weichun; Kolomeisky, Anatoly B.; Vekilov, Peter G.

2005-05-01

31

A Theoretical Study of Vapour Phase Nucleation of the Rocket Propellant N2O4  

NASA Astrophysics Data System (ADS)

The residual vapour of a rocket fuel at the venting stage develops a potential aerodynamic problem which is linked with the vapour phase nucleation phenomena of the propellant. This study, based entirely on molecular treatment, addresses the problem by focusing specifically on the N2O4 propellant which is used in the ARIANE flight. The phenomenon is examined by considering the thermodynamic free energies of N2O4 clusters, leading to the evaluation of nucleation flux rates of critical nuclei at incipient nucleation. Preliminary examinations of the kinetics of flux pulses provide basic explanation from a molecular perspective.

Pal, P.

2003-05-01

32

Role of Dynamic Nucleation at Moving Boundaries in Phase and Microstructure Selection  

NASA Technical Reports Server (NTRS)

Solidification microstructures that form under steady-state growth conditions (cells, dendrites, regular eutectics, etc.) are reasonably well understood in comparison to other, more complex microstructures, which form under intrinsically non-steady-state growth conditions due to the competition between the nucleation and growth of several phases. Some important practical examples in this latter class include microstructures forming in peritectic systems in highly undercooled droplets, and in strip cast stainless steels. Prediction of phase and microstructure selection in these systems has been traditionally based on (1) heterogeneous nucleation on a static interface, and (2) comparing the relative growth rate of different phase/microstructures under steady-state growth conditions. The formation of new phases, however, occurs via nucleation on, or ahead of, a moving boundary. In addition, the actual selection process is controlled by a complex interaction between the nucleation process and the growth competition between the nuclei and the pre-existing phase under non-steady-state conditions. As a result, it is often difficult to predict which microstructure will form and which phases will be selected under prescribed processing conditions. This research addresses this critical role of nucleation at moving boundaries in the selection of phases and solidification microstructures through quantitative experiments and numerical modeling in peritectic systems. In order to create a well characterized system in which to study this problem, we focus on the directional solidification of hypo- and hyper-peritectic alloys in the two-phase region, imposing a large enough ratio of temperature gradient/growth rate (G/V(sub p)) to suppress the morphological instability of both the parent (alpha) and peritectic (Beta) phases, i.e. each phase alone would grow as a planar front. Our combined experimental and theoretical results show that, already in this simplified case, the growth competition of these two phases leads to a rich variety of microstructures that depend sensitively upon the relative importance of nucleation, diffusion, and convection.

Karma, Alain; Trivedi, Rohit

1999-01-01

33

Competition of homogeneous and heterogeneous ice nucleation on secondary organic aerosol particles: The role of particle phase state  

NASA Astrophysics Data System (ADS)

Recently, secondary organic aerosol (SOA) particles have been found to exhibit a highly viscous, amorphous state under atmospherically relevant conditions (Virtanen et al., 2010). Besides retardation of chemical reactions (Shiraiwa et al., 2011) and incomplete gas-to-particle partitioning of semi-volatile constituents (Vaden et al., 2011), these particles were found to suppress homogeneous ice nucleation (Murray et al., 2008), which normally takes place when a liquid particle reaches its respective homogeneous nucleation limit (Koop et al., 2000). In turn, glassy SOA particles may act themselves as heterogeneous ice nuclei as recent studies suggest (e.g. Murray et al., 2010, Wang et al., 2012). The predominant nucleation pathway for SOA particles is thus controlled by particle phase state. The phase state of SOA particles depends on several factors such as composition, temperature and relative humidity. In atmospheric updrafts, inducing a change in temperature and relative humidity, moisture- and temperature-induced phase transitions can occur (e.g. Shiraiwa et al., 2011). In fast updrafts, these particles may also deviate from humidification equilibrium, i.e. the agreement between ambient relative humidity and water activity inside the particle may not be established at any point in time. The extent of this temporal delay is governed by the updraft velocity, the particle size and the diffusivity of water inside the glassy organic particle matrix. Here we show how the delayed deliquescence of SOA particles can be quantified for SOA from a variety of precursors. A kinetic flux model (Shiraiwa et al., 2012) is applied and the predominant ice nucleation pathway is inferred from particle phase state at the respective homogeneous and heterogeneous nucleation limits. To estimate diffusivities inside the organic particle matrix for the relevant range of temperature and humidity, we developed a novel method that relies on glass transition and hygroscopic growth data that are more easily available. The model simulations suggest upper temperature boundaries, below which heterogeneous ice nucleation of glassy aerosols may occur, depending on updraft velocities and particle size. We also show that the predominant ice nucleation pathway depends on precursor material and oxidation state. References Koop, T. et al. (2000) Nature 406, 611. Murray, B. J. (2008) Atmos. Chem. Phys. 8, 5423. Murray, B. J. et al. (2010) Nature Geosci. 3, 233. Shiraiwa, M. et al. (2011) Proc. Natl. Acad. Sci. 108, 11003. Shiraiwa, M. et al. (2012) Atmos. Chem. Phys. 12, 2777. Virtanen, A. et al. (2010) Nature 467, 824. Vaden, T. D. et al. (2011) Proc. Natl. Acad. Sci., 108, 2190. Wang, B. et al. (2012) J. Geophys. Res., 117, D16209.

Berkemeier, Thomas; Shiraiwa, Manabu; Pöschl, Ulrich; Koop, Thomas

2014-05-01

34

Localized Orientational Order Chaperones the Nucleation of Rotator Phases in Hard Polyhedral Particles  

NASA Astrophysics Data System (ADS)

The nucleation kinetics of the rotator phase in hard cuboctahedra, truncated octahedra, and rhombic dodecahedra is simulated via a combination of forward flux sampling and umbrella sampling. For comparable degrees of supersaturation, the polyhedra are found to have significantly lower free-energy barriers and faster nucleation rates than hard spheres. This difference primarily stems from localized orientational ordering, which steers polyhedral particles to pack more efficiently. Orientational order hence fosters here the growth of orientationally disordered nuclei.

Thapar, Vikram; Escobedo, Fernando A.

2014-01-01

35

Role of Nucleation and Growth in Two-Phase Microstructure Formation  

SciTech Connect

During the directional solidification of peritectic alloys, a rich variety of two-phase microstructures develop, and the selection process of a specific microstructure is complicated due to the following two considerations. (1) In contrast to many single phase and eutectic microstructures that grow under steady state conditions, two-phase microstructures in a peritectic system often evolve under non-steady-state conditions that can lead to oscillatory microstructures, and (2) the microstructure is often governed by both the nucleation and the competitive growth of the two phases in which repeated nucleation can occur due to the change in the local conditions during growth. In this research, experimental studies in the Sn-Cd system were designed to isolate the effects of nucleation and competitive growth on the dynamics of complex microstructure formation. Experiments were carried out in capillary samples to obtain diffusive growth conditions so that the results can be analyzed quantitatively. At high thermal gradient and low velocity, oscillatory microstructures were observed in which repeated nucleation of the two phases was observed at the wall-solid-liquid junction. Quantitative measurements of nucleation undercooling were obtained for both the primary and the peritectic phase nucleation, and three different ampoule materials were used to examine the effect of different contact angles at the wall on nucleation undercooling. Nucleation undercooling for each phase was found to be very small, and the experimental undercooling values were orders of magnitude smaller than that predicted by the classical theory of nucleation. A new nucleation mechanism is proposed in which the clusters of atoms at the wall ahead of the interface can become a critical nucleus when the cluster encounters the triple junction. Once the nucleation of a new phase occurs, the microstructure is found to be controlled by the relative growth of the two phases that give rise to different oscillatory microstructures that depend on the imposed velocity and the size of the sample. At low thermal gradient to velocity ratio, a steady-state composite microstructure is observed. Two mechanisms of composite microstructure formation were examined: (1) the formation of the peritectic phase in the intercellular region of the primary phase where the solute rejected by the primary phase is absorbed by the peritectic phase. The peritectic phase forms a small distance behind the growing primary phase front. (2) The second mechanism is the coupled growth of the two phases with a macroscopically planar interface, as in the case of eutectic growth. Detailed studies showed that this composite microstructure, although it appears as a eutectic microstructure, did not grow in the coupled manner at the advancing interface in the Sn-cd system. However, a new observation was made when experiments were carried out in thin ampoule of Ta. The peritectic phase nucleated at the wall-interface triple junction and grew along the wall, while the primary phase continued to grow at the center, giving rise to a steady-state couple growth at some specific velocity. The mechanism of coupled growth in this case was shown to be operative due to the presence of a finite contact angle at the wall, and this was demonstrated by including the contact angle effect at the wall in the rod eutectic growth model. The experimental results were summarized to map out the conditions of thermal gradient and velocity on the regimes of composite and oscillatory microstructure formation. The formation of complex time-dependent microstructures was then discussed in terms of the time-dependent dynamics of planar interface growth.

Jong Ho Shin

2008-05-01

36

Role of nucleation and growth in two-phase microstructure formation  

NASA Astrophysics Data System (ADS)

During the directional solidification of peritectic alloys, a rich variety of two-phase microstructures develop, and the selection process of a specific microstructure is complicated due to the following two considerations. (1) In contrast to many single phase and eutectic microstructures that grow under steady state conditions, two-phase microstructures in a peritectic system often evolve under non-steady-state conditions that can lead to oscillatory microstructures, and (2) the microstructure is often governed by both the nucleation and the competitive growth of the two phases in which repeated nucleation can occur due to the change in the local conditions during growth. In this research, experimental studies in the Sn-Cd system were designed to isolate the effects of nucleation and competitive growth on the dynamics of complex microstructure formation. Experiments were carried out in capillary samples to obtain diffusive growth conditions so that the results can be analyzed quantitatively. At high thermal gradient and low velocity, oscillatory microstructures were observed in which repeated nucleation of the two phases was observed at the wall-solid-liquid junction. Quantitative measurements of nucleation undercooling were obtained for both the primary and the peritectic phase nucleation, and three different ampoule materials were used to examine the effect of different contact angles at the wall on nucleation undercooling. Nucleation undercooling for each phase was found to be very small, and the experimental undercooling values were orders of magnitude smaller than that predicted by the classical theory of nucleation. A new nucleation mechanism is proposed in which the clusters of atoms at the wall ahead of the interface can become a critical nucleus when the cluster encounters the triple junction. Once the nucleation of a new phase occurs, the microstructure is found to be controlled by the relative growth of the two phases that give rise to different oscillatory microstructures that depend on the imposed velocity and the size of the sample. At low thermal gradient to velocity ratio, a steady-state composite microstructure is observed. Two mechanisms of composite microstructure formation were examined: (i) the formation of the peritectic phase in the intercellular region of the primary phase where the solute rejected by the primary phase is absorbed by the peritectic phase. The peritectic phase forms a small distance behind the growing primary phase front. (ii) The second mechanism is the coupled growth of the two phases with a macroscopically planar interface, as in the case of eutectic growth. Detailed studies showed that this composite microstructure, although it appears as a eutectic microstructure, did not grow in the coupled manner at the advancing interface in the Sn-Cd system. However, a new observation was made when experiments were carried out in thin ampoule of Ta. The peritectic phase nucleated at the wall-interface triple junction and grew along the wall, while the primary phase continued to grow at the center, giving rise to a steady-state couple growth at some specific velocity. The mechanism of coupled growth in this case was shown to be operative due to the presence of a finite contact angle at the wall, and this was demonstrated by including the contact angle effect at the wall in the rod eutectic growth model. The experimental results were summarized to map out the conditions of thermal gradient and velocity on the regimes of composite and oscillatory microstructure formation. The formation of complex time-dependent microstructures was then discussed in terms of the time-dependent dynamics of planar interface growth.

Shin, Jong Ho

37

Ice nucleation by combustion ash particles at conditions relevant to mixed-phase clouds  

NASA Astrophysics Data System (ADS)

Ice nucleating particles can modify cloud properties with implications for climate and the hydrological cycle; hence, it is important to understand which aerosol particle types nucleate ice and how efficiently they do so. It has been shown that aerosol particles such as natural dusts, volcanic ash, bacteria and pollen can act as ice nucleating particles, but the ice nucleating ability of combustion ashes has not been studied. Combustion ashes are major by-products released during the combustion of solid fuels and a significant amount of these ashes are emitted into the atmosphere either during combustion or via aerosolization of bottom ashes. Here, we show that combustion ashes (coal fly ash, wood bottom ash, domestic bottom ash, and coal bottom ash) nucleate ice in the immersion mode at conditions relevant to mixed-phase clouds. Hence, combustion ashes could play an important role in primary ice formation in mixed-phase clouds, especially in clouds that are formed near the emission source of these aerosol particles. In order to quantitatively assess the impact of combustion ashes on mixed-phase clouds, we propose that the atmospheric abundance of combustion ashes should be quantified since up to now they have mostly been classified together with mineral dust particles. Also, in reporting ice residue compositions, a distinction should be made between natural mineral dusts and combustion ashes in order to quantify the contribution of combustion ashes to atmospheric ice nucleation.

Umo, N. S.; Murray, B. J.; Baeza-Romero, M. T.; Jones, J. M.; Lea-Langton, A. R.; Malkin, T. L.; O'Sullivan, D.; Plane, J. M. C.; Williams, A.

2014-11-01

38

Two-step nucleation mechanism in solid–solid phase transitions  

NASA Astrophysics Data System (ADS)

The microscopic kinetics of ubiquitous solid–solid phase transitions remain poorly understood. Here, by using single-particle-resolution video microscopy of colloidal films of diameter-tunable microspheres, we show that transitions between square and triangular lattices occur via a two-step diffusive nucleation pathway involving liquid nuclei. The nucleation pathway is favoured over the direct one-step nucleation because the energy of the solid/liquid interface is lower than that between solid phases. We also observed that nucleation precursors are particle-swapping loops rather than newly generated structural defects, and that coherent and incoherent facets of the evolving nuclei exhibit different energies and growth rates that can markedly alter the nucleation kinetics. Our findings suggest that an intermediate liquid should exist in the nucleation processes of solid–solid transitions of most metals and alloys, and provide guidance for better control of the kinetics of the transition and for future refinements of solid–solid transition theory.

Peng, Yi; Wang, Feng; Wang, Ziren; Alsayed, Ahmed M.; Zhang, Zexin; Yodh, Arjun G.; Han, Yilong

2015-01-01

39

Homogeneous nucleation rate measurements of 1-propanol in helium: the effect of carrier gas pressure.  

PubMed

Kinetics of homogeneous nucleation in supersaturated vapor of 1-propanol was studied using an upward thermal diffusion cloud chamber. Helium was used as a noncondensable carrier gas and the influence of its pressure on observed nucleation rates was investigated. The isothermal nucleation rates were determined by a photographic method that is independent on any nucleation theory. In this method, the trajectories of growing droplets are recorded using a charge coupled device camera and the distribution of local nucleation rates is determined by image analysis. The nucleation rate measurements of 1-propanol were carried out at four isotherms 260, 270, 280, and 290 K. In addition, the pressure dependence was investigated on the isotherms 290 K (50, 120, and 180 kPa) and 280 K (50 and 120 kPa). The isotherm 270 K was measured at 25 kPa and the isotherm 260 K at 20 kPa. The experiments confirm the earlier observations from several thermal diffusion chamber investigations that the homogeneous nucleation rate of 1-propanol tends to increase with decreasing total pressure in the chamber. In order to reduce the possibility that the observed phenomenon is an experimental artifact, connected with the generally used one-dimensional description of transfer processes in the chamber, a recently developed two-dimensional model of coupled heat, mass, and momentum transfer inside the chamber was used and results of both models were compared. It can be concluded that the implementation of the two-dimensional model does not explain the observed effect. Furthermore the obtained results were compared both to the predictions of the classical theory and to the results of other investigators using different experimental devices. Plotting the experimental data on the so-called Hale plot shows that our data seem to be consistent both internally and also with the data of others. Using the nucleation theorem the critical cluster sizes were obtained from the slopes of the individual isotherms and compared with the Kelvin prediction. The influence of total pressure on the observed isothermal nucleation rate was studied in another experiment, where not only temperature but also supersaturation was kept constant as the total pressure was changed. It was shown that the dependence of the nucleation rate on pressure gets stronger as pressure decreases. PMID:16674134

Brus, David; Zdímal, Vladimír; Stratmann, Frank

2006-04-28

40

Helmholtz free energy of a phase containing a sparse ensemble of heterophase clusters with application to nucleation theory.  

PubMed

A decomposition of the Helmholtz free energy of a phase containing a sparse ensemble of heterophase clusters is derived based on classical statistical mechanics and on the general physical characteristics of such systems. It is not assumed that the phase is an ideal gas. The building blocks of this decomposition are the Helmholtz free energies of the constituents (phase and stationary heterophase clusters) and, for every cluster species, a volume V(k)(cm), which is of the magnitude of the thermal fluctuation volume of the center of mass of the stationary cluster containing k monomers. A definition of V(k)(cm) is given in terms of the configuration integrals of the clusters. V(k)(cm) is evaluated for k > 1, with the result that V(k)(cm) is proportional to k(-1/2) and is a function of temperature, the specific volume, and the isothermal compressibility of the phase in the cluster. A thermodynamically consistent expression for the work to form a stationary cluster, which reads as Delta g(k)/(k(B)T) = -ak + (3/2)bk(2/3) + 3ck(1/3) + d, is derived. The coefficients a, b, c, and d depend on the thermodynamic properties of the homogeneous phases, on the surface tension, and on one additional phenomenological material function of temperature and pressure. The description is general and covers a wide class of materials. It is shown that the heterogeneous system represents the thermodynamic equilibrium and not the pure phase without clusters. The resulting expression for the equilibrium particle number, which is different from the one used in classical nucleation theory, is by a standard procedure input for the calculation of the stationary Becker-Döring nucleation rate and entails a correction factor for the classical nucleation rate. Comparison with experiments is provided for nucleation onset measurements of argon and for measurements of the homogeneous nucleation rate of water. Measurements and theory can be brought to match within the limits of experimental precision in both cases. PMID:20148535

Tschudi, Hans Rudolf

2010-03-11

41

Nucleation mechanism for the direct graphite-to-diamond phase transition  

E-print Network

Graphite and diamond have comparable free energies, yet forming diamond from graphite is far from easy. In the absence of a catalyst, pressures that are significantly higher than the equilibrium coexistence pressures are required to induce the graphite-to-diamond transition. Furthermore, the formation of the metastable hexagonal polymorph of diamond instead of the more stable cubic diamond is favored at lower temperatures. The concerted mechanism suggested in previous theoretical studies cannot explain these phenomena. Using an ab initio quality neural-network potential we performed a large-scale study of the graphite-to-diamond transition assuming that it occurs via nucleation. The nucleation mechanism accounts for the observed phenomenology and reveals its microscopic origins. We demonstrated that the large lattice distortions that accompany the formation of the diamond nuclei inhibit the phase transition at low pressure and direct it towards the hexagonal diamond phase at higher pressure. The nucleation me...

Khaliullin, Rustam Z; Kuhne, Thomas D; Behler, Jorg; Parrinello, Michele

2011-01-01

42

Nucleation mechanism for the direct graphite-to-diamond phase transition  

NASA Astrophysics Data System (ADS)

Graphite and diamond have comparable free energies, yet forming diamond from graphite in the absence of a catalyst requires pressures that are significantly higher than those at equilibrium coexistence. At lower temperatures, the formation of the metastable hexagonal polymorph of diamond is favoured instead of the more stable cubic diamond. These phenomena cannot be explained by the concerted mechanism suggested in previous theoretical studies. Using an ab initio quality neural-network potential, we carried out a large-scale study of the graphite-to-diamond transition assuming that it occurs through nucleation. The nucleation mechanism accounts for the observed phenomenology and reveals its microscopic origins. We demonstrate that the large lattice distortions that accompany the formation of diamond nuclei inhibit the phase transition at low pressure, and direct it towards the hexagonal diamond phase at higher pressure. The proposed nucleation mechanism should improve our understanding of structural transformations in a wide range of carbon-based materials.

Khaliullin, Rustam Z.; Eshet, Hagai; Kühne, Thomas D.; Behler, Jörg; Parrinello, Michele

2011-09-01

43

NUCLEATION, KINETICS AND ADMISSIBILITY CRITERIA FOR PROPAGATING PHASE BOUNDARIES  

E-print Network

;es a critical value of f at an incipient phase boundary. We then incorporate inertial eects, and we of longitudinal motions of an elastic bar, one considers a pair of conservation laws in one space dimension in dynamics, but in the theory of phase transitions in quasi-static motions as well. In [2], we viewed

44

NUCLEATION, KINETICS AND ADMISSIBILITY CRITERIA FOR PROPAGATING PHASE BOUNDARIES  

E-print Network

specifies a critical value of f at an incipient phase boundary. We then incorporate inertial effects, and we of longitudinal motions of an elastic bar, one considers a pair of conservation laws in one space dimension in quasi­static motions as well. In [2], we

45

Quantized hard-x-ray phase vortices nucleated by aberrated nanolenses  

SciTech Connect

Quantized x-ray phase vortices, namely, screw-type topological defects in the wave fronts of a coherent monochromatic scalar x-ray wave field, may be spontaneously nucleated by x-ray lenses. Phase retrieval is used to reconstruct the phase and amplitude of the complex disturbance created by aberrated gold nanolenses illuminated with hard x rays. A nanoscale quantized x-ray vortex-antivortex dipole is observed, manifest both as a pair of opposite-helicity branch points in the Riemann sheets of the multivalued x-ray phase map of the complex x-ray field and in the vorticity of the associated Poynting vector field.

Pavlov, Konstantin M. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); School of Physics, Monash University, Victoria 3800 (Australia); Paganin, David M. [School of Physics, Monash University, Victoria 3800 (Australia); Vine, David J. [ARC Centre of Excellence for Coherent X-ray Science, School of Physics, The University of Melbourne, Parkville, Victoria 3010 (Australia); Schmalz, Jelena A. [School of Science and Technology, University of New England, Armidale, New South Wales 2351 (Australia); Suzuki, Yoshio; Uesugi, Kentaro; Takeuchi, Akihisa; Yagi, Naoto [SPring-8/JASRI (Japan Synchrotron Radiation Research Institute), Hyogo 679-5198 (Japan); Kharchenko, Alexander; Blaj, Gabriel [PANalytical B.V., P.O. Box 13, 7600 AA Almelo (Netherlands); Jakubek, Jan [Institute of Experimental and Applied Physics, Czech Technical University in Prague, 166 36 Prague 6 (Czech Republic); Altissimo, Matteo [Melbourne Centre for Nanofabrication, 151 Wellington Road, Clayton, Victoria 3168 (Australia); Materials Science and Engineering, Commonwealth Scientific and Industrial Research Organisation, Clayton South, Victoria 3169 (Australia); Clark, Jesse N. [London Centre for Nanotechnology, University College, Gower St, London WC1E 6BT (United Kingdom)

2011-01-15

46

The carrier gas pressure effect in a laminar flow diffusion chamber, homogeneous nucleation of n-butanol in helium.  

PubMed

Homogeneous nucleation rate isotherms of n-butanol+helium were measured in a laminar flow diffusion chamber at total pressures ranging from 50 to 210 kPa to investigate the effect of carrier gas pressure on nucleation. Nucleation temperatures ranged from 265 to 280 K and the measured nucleation rates were between 10(2) and 10(6) cm(-3) s(-1). The measured nucleation rates decreased as a function of increasing pressure. The pressure effect was strongest at pressures below 100 kPa. This negative carrier gas effect was also temperature dependent. At nucleation temperature of 280 K and at the same saturation ratio, the maximum deviation between nucleation rates measured at 50 and 210 kPa was about three orders of magnitude. At nucleation temperature of 265 K, the effect was negligible. Qualitatively the results resemble those measured in a thermal diffusion cloud chamber. Also the slopes of the isothermal nucleation rates as a function of saturation ratio were different as a function of total pressure, 50 kPa isotherms yielded the steepest slopes, and 210 kPa isotherms the shallowest slopes. Several sources of inaccuracies were considered in the interpretation of the results: uncertainties in the transport properties, nonideal behavior of the vapor-carrier gas mixture, and shortcomings of the used mathematical model. Operation characteristics of the laminar flow diffusion chamber at both under-and over-pressure were determined to verify a correct and stable operation of the device. We conclude that a negative carrier gas pressure effect is seen in the laminar flow diffusion chamber and it cannot be totally explained with the aforementioned reasons. PMID:16784271

Hyvärinen, Antti-Pekka; Brus, David; Zdímal, Vladimír; Smolík, Jiri; Kulmala, Markku; Viisanen, Yrjö; Lihavainen, Heikki

2006-06-14

47

Ice Nucleation in a Venus Atmosphere  

Microsoft Academic Search

The possible phase of Venus cloud particles has been experimentally studied. Carbon dioxide gas of 0.83 atm held in a uniform temperature mixing cloud chamber was used as a simulated Venus atmosphere at the condensation level. The ice nucleating behavior of some artificial and natural ice nuclei were tested. The heterogenous and homogeneous ice nucleation temperatures in the CO2 atmosphere

N. Fukuta; T.-L. Wang; W. F. Libby

1969-01-01

48

Ion-induced nucleation in polar one-component fluids Hikaru Kitamuraa  

E-print Network

Ion-induced nucleation in polar one-component fluids Hikaru Kitamuraa and Akira Onuki Department-Landau theory of ion-induced nucleation in polar one-component flu- ids in a gas phase. It will be based on our; published online 27 September 2005 We present a Ginzburg-Landau theory of ion-induced nucleation in a gas

49

Gas-phase chemical dynamics  

SciTech Connect

Research in this program is directed towards the spectroscopy of small free radicals and reactive molecules and the state-to-state dynamics of gas phase collision, energy transfer, and photodissociation phenomena. Work on several systems is summarized here.

Weston, R.E. Jr.; Sears, T.J.; Preses, J.M. [Brookhaven National Laboratory, Upton, NY (United States)

1993-12-01

50

Microphysical Consequences of the Spatial Distribution of Ice Nucleation in Mixed-Phase Stratiform Clouds  

SciTech Connect

Mixed-phase stratiform clouds can persist even with steady ice precipitation fluxes, and the origin and microphysical properties of the ice crystals are of interest. Vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation, leads to a power law relation between ice water content wi and ice number concentration ni with exponent 2.5. The result is independent of assumptions about the vertical velocity structure of the cloud and is therefore more general than the related expression of Yang et al. [2013]. The sensitivity of the wi-ni relationship to the spatial distribution of ice nucleation is confirmed by Lagrangian tracking and ice growth with cloud-volume, cloud-top, and cloud-base sources of ice particles through a time-dependent cloud field. Based on observed wi and ni from ISDAC, a lower bound of 0.006 m^3/s is obtained for the ice crystal formation rate.

Yang, Fan; Ovchinnikov, Mikhail; Shaw, Raymond A.

2014-07-28

51

Heterogeneous ice nucleation on phase-separated organic-sulfate particles: effect of liquid vs. glassy coatings  

NASA Astrophysics Data System (ADS)

Atmospheric ice nucleation on aerosol particles relevant to cirrus clouds remains one of the least understood processes in the atmosphere. Upper tropospheric aerosols as well as sub-visible cirrus residues are known to be enhanced in both sulfates and organics. The hygroscopic phase transitions of organic-sulfate particles can have an impact on both the cirrus cloud formation mechanism and resulting cloud microphysical properties. In addition to deliquescence and efflorescence, organic-sulfate particles are known to undergo another phase transition known as liquid-liquid phase separation. The ice nucleation properties of particles that have undergone liquid-liquid phase separation are unknown. Here, Raman microscopy coupled with an environmental cell was used to study the low temperature deliquescence, efflorescence, and liquid-liquid phase separation behavior of 2 : 1 mixtures of organic polyols (1,2,6-hexanetriol and 1 : 1 1,2,6-hexanetriol + 2,2,6,6-tetrakis(hydroxymethyl)cyclohexanol) and ammonium sulfate from 240-265 K. Further, the ice nucleation efficiency of these organic-sulfate systems after liquid-liquid phase separation and efflorescence was investigated from 210-235 K. Raman mapping and volume-geometry analysis indicate that these particles contain solid ammonium sulfate cores fully engulfed in organic shells. For the ice nucleation experiments, we find that if the organic coatings are liquid, water vapor diffuses through the shell and ice nucleates on the ammonium sulfate core. In this case, the coatings minimally affect the ice nucleation efficiency of ammonium sulfate. In contrast, if the coatings become semi-solid or glassy, ice instead nucleates on the organic shell. Consistent with recent findings that glasses can be efficient ice nuclei, the phase-separated particles are nearly as efficient at ice nucleation as pure crystalline ammonium sulfate.

Schill, G. P.; Tolbert, M. A.

2013-05-01

52

Classical nucleation theory with a radius-dependent surface tension: a two-dimensional lattice-gas automata model.  

PubMed

The constant surface tension assumption of the Classical Nucleation Theory (CNT) is known to be flawed. In order to probe beyond this limitation, we consider a microscopic, two-dimensional Lattice-Gas Automata (LGA) model of nucleation in a supersaturated system, with model input parameters E(ss) (solid particle-to-solid particle bonding energy), E(sw) (solid particle-to-water bonding energy), ? (next-to-nearest-neighbor bonding coefficient in solid phase), and C(in) (initial solute concentration). The LGA method has the advantages of easy implementation, low memory requirements, and fast computation speed. Analytical results for the system's concentration and the crystal radius as functions of time are derived and the former is fit to the simulation data in order to determine the equilibrium concentration. The "Mean First-Passage Time" technique is used to obtain the nucleation rate and critical nucleus size from the simulation data. The nucleation rate and supersaturation data are evaluated using a modification to the CNT that incorporates a two-dimensional radius-dependent surface tension term. The Tolman parameter, ?, which controls the radius dependence of the surface tension, decreases (increases) as a function of the magnitude of E(ss) (E(sw)), at fixed values of ? and E(sw) (E(ss)). On the other hand, ? increases as ? increases while E(ss) and E(sw) are held constant. The constant surface tension term of the CNT, ?(0), increases (decreases) with increasing magnitudes of E(ss) (E(sw)) at fixed values of E(sw) (E(ss)) and increases as ? is increased. ?(0) increases linearly as a function of the change in energy during an attachment or detachment reaction, |?E|, however, with a slope less than that predicted for a crystal that is uniformly packed at maximum density. These results indicate an increase in the radius-dependent surface tension, ?, with respect to increasing magnitude of the difference between E(ss) and E(sw). PMID:23496525

Hickey, Joseph; L'Heureux, Ivan

2013-02-01

53

An Effective Continuum Model for the Liquid-to-Gas Phase Change in a Porous Medium Driven by Solute Diffusion: II. Constant Liquid Withdrawal Rates  

SciTech Connect

This report describes the development of an effective continuum model to describe the nucleation and subsequent growth of a gas phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute diffusion.This report also focuses on the processes resulting from the withdrawal of the liquid at a constant rate. As before, the model addresses two stages before the onset of bulk gas flow, nucleation and gas phase growth. Because of negligible gradients due to gravity or viscous forces, the critical gas saturation, is only a function of the nucleation fraction.

Tsimpanogiannis, Ioannis N.; Yortsos, Yanis C.

2001-08-15

54

On the theory of transient nucleation at the intermediate stage of phase transitions  

NASA Astrophysics Data System (ADS)

The evolution of a system of growing aggregates in a macroscopically homogeneous medium with account of both the reduction in metastability and the continuing initiation of new nuclei is studied. The corresponding integro-differential model describing the intermediate stage of phase transitions is solved analytically for arbitrary nucleation kinetics and growth rates of nuclei. An exact solution of the Fokker-Planck equation is found with allowance for the diffusivity along the axis of nucleus radii. In limiting cases of purely kinetic and mixed kinetic-diffusion rates of crystal growth for a special form of diffusivity, the obtained solutions transform to earlier known expressions.

Alexandrov, D. V.

2014-04-01

55

Report on the Implementation of Homogeneous Nucleation Scheme in MARMOT-based Phase Field Simulation  

SciTech Connect

In this report, we summarized our effort in developing mesoscale phase field models for predicting precipitation kinetics in alloys during thermal aging and/or under irradiation in nuclear reactors. The first part focused on developing a method to predict the thermodynamic properties of critical nuclei such as the sizes and concentration profiles of critical nuclei, and nucleation barrier. These properties are crucial for quantitative simulations of precipitate evolution kinetics with phase field models. Fe-Cr alloy was chosen as a model alloy because it has valid thermodynamic and kinetic data as well as it is an important structural material in nuclear reactors. A constrained shrinking dimer dynamics (CSDD) method was developed to search for the energy minimum path during nucleation. With the method we are able to predict the concentration profiles of the critical nuclei of Cr-rich precipitates and nucleation energy barriers. Simulations showed that Cr concentration distribution in the critical nucleus strongly depends on the overall Cr concentration as well as temperature. The Cr concentration inside the critical nucleus is much smaller than the equilibrium concentration calculated by the equilibrium phase diagram. This implies that a non-classical nucleation theory should be used to deal with the nucleation of Cr precipitates in Fe-Cr alloys. The growth kinetics of both classical and non-classical nuclei was investigated by the phase field approach. A number of interesting phenomena were observed from the simulations: 1) a critical classical nucleus first shrinks toward its non-classical nucleus and then grows; 2) a non-classical nucleus has much slower growth kinetics at its earlier growth stage compared to the diffusion-controlled growth kinetics. 3) a critical classical nucleus grows faster at the earlier growth stage than the non-classical nucleus. All of these results demonstrated that it is critical to introduce the correct critical nuclei into phase field modeling in order to correctly capture the kinetics of precipitation. In most alloys the matrix phase and precipitate phase have different concentrations as well as different crystal structures. For example, Cu precipitates in FeCu alloys have fcc crystal structure while the matrix Fe-Cu solid solution has bcc structure at low temperature. The WBM model and KimS model, where both concentrations and order parameters are chosen to describe the microstructures, are commonly used to model precipitations in such alloys. The WBM and KimS models have not been implemented into Marmot yet. In the second part of this report, we focused on implementing the WBM and KimS models into Marmot. The Fe-Cu alloys, which are important structure materials in nuclear reactors, was taken as the model alloys to test the models.

Li, Yulan; Hu, Shenyang Y.; Sun, Xin

2013-09-30

56

Nanoscale Phase Stability Reversal During the Nucleation and Growth of Titanium Oxide Minerals  

NASA Astrophysics Data System (ADS)

Fine-grained titanium oxide minerals are important in soils, where they affect a variety of geochemical processes. They are also industrially important as catalysts, pigments, food additives, and dielectrics. Recent research has indicated an apparent reversal of thermodynamic stability between TiO2 phases at the nanoscale thought to be caused by an increased contribution of surface energy to the total free energy. Time-resolved X-ray diffraction (XRD) experiments in which titanium oxides crystallize from aqueous TiCl4 solutions confirm that anatase, a metastable phase, is always the first phase to nucleate under our range of initial conditions. Rutile peaks are observed only minutes after the first appearance of anatase, after which anatase abundance slowly decreases while rutile continues to form. Whole pattern refinement of diffraction data reveals that lattice constants of both phases increase throughout the crystallization process. In addition, transmission electron microscope (TEM) observations and kinetic modeling indicate that anatase does not undergo a solid-state transformation to the rutile structure as once thought. Instead, anatase appears to re-dissolve and then feed the growth of already nucleated rutile nanocrystals. Density functional theory (DFT) calculations were employed to model 1, 2, and 3 nm particles of both mineral phases. The total surface energies calculated from these models did yield lower values for anatase than for rutile by 8-13 kJ/mol depending on particle size, indicating that surface free energy is sufficient to account for stability reversal. However, these whole-particle surface energies were much higher than the sum of energies of each particle's constituent crystallographic surfaces. We attribute the excess energy to defects associated with the edges and corners of nanoparticles, which are not present on a 2-D periodic surface. This previously unreported edge and corner energy may play a dominant role in the stability reversal of nanocrystalline titanium oxides, as well as other mineral systems susceptible to reversals in phase stability at the nanoscale.

Hummmer, D. R.; Heaney, P. J.; Kubicki, J. D.; Kent, P. R.; Post, J. E.

2008-12-01

57

Gas phase atmospheric bromine photochemistry  

Microsoft Academic Search

This paper reviews the current knowledge of gas phase bromine photochemistry and presents a budget study of atmospheric bromine species. The effectiveness of the ozone catalytic loss cycles involving bromine is quantified by considering their chain length and effectiveness. The chain effectiveness is a new variable defined as the chain length multiplied by the rate of the cycle's rate-limiting step.

D. J. Lary

1996-01-01

58

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

The local atomic structures of undercooled liquid metals are presumed to be icosahedral; this order is incompatible with translational periodicity, constituting a barrier to the nucleation of the crystal phase. The extended atomic structure of the icosahedral quasicrystal (i-phase) is similar to that presumed in the undercooled liquid. Therefore, a comparison of the maximum undercooling in alloys that form the i-phase with those that form crystal phases provides a probe of the liquid structure.

Kelton, K. F.; Gangopadhyay, A. K.; Lee, G. W.; Hyers, R. W.; Rogers, J. R.; Robinson, M. B.; Rathz, T. J.; Krishnan, S.; Curreri, Peter A. (Technical Monitor)

2002-01-01

59

Cluster Nucleation and Growth from a Highly Supersaturated Adatom Phase: Silver on Magnetite  

PubMed Central

The atomic-scale mechanisms underlying the growth of Ag on the (?2×?2)R45°-Fe3O4(001) surface were studied using scanning tunneling microscopy and density functional theory based calculations. For coverages up to 0.5 ML, Ag adatoms populate the surface exclusively; agglomeration into nanoparticles occurs only with the lifting of the reconstruction at 720 K. Above 0.5 ML, Ag clusters nucleate spontaneously and grow at the expense of the surrounding material with mild annealing. This unusual behavior results from a kinetic barrier associated with the (?2×?2)R45° reconstruction, which prevents adatoms from transitioning to the thermodynamically favorable 3D phase. The barrier is identified as the large separation between stable adsorption sites, which prevents homogeneous cluster nucleation and the instability of the Ag dimer against decay to two adatoms. Since the system is dominated by kinetics as long as the (?2×?2)R45° reconstruction exists, the growth is not well described by the traditional growth modes. It can be understood, however, as the result of supersaturation within an adsorption template system. PMID:24945923

2014-01-01

60

Microphysical consequences of the spatial distribution of ice nucleation in mixed-phase stratiform clouds  

NASA Astrophysics Data System (ADS)

Mixed-phase stratiform clouds can persist even with steady ice precipitation fluxes, and the origin and microphysical properties of the ice crystals are of interest. Vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation lead to a power law relation between ice water content wi and ice number concentration ni with exponent 2.5. The result is independent of assumptions about the vertical velocity structure of the cloud and is therefore more general than the related expression of Yang et al. (2013). The sensitivity of the wi-ni relationship to the spatial distribution of ice nucleation is confirmed by Lagrangian tracking and ice growth with cloud volume, cloud top, and cloud base sources of ice particles through a time-dependent cloud field. Based on observed wi and ni from Indirect and Semi-Direct Aerosol Campaign, a lower bound of 0.006 m-3 s-1 is obtained for the ice crystal formation rate.

Yang, Fan; Ovchinnikov, Mikhail; Shaw, Raymond A.

2014-07-01

61

Direct numerical simulation of homogeneous nucleation and growth in a phase-field model using cell dynamics method  

NASA Astrophysics Data System (ADS)

The homogeneous nucleation and growth in a simplest two-dimensional phase field model is numerically studied using the cell dynamics method. The whole process from nucleation to growth is simulated and is shown to follow closely the Kolmogorov-Johnson-Mehl-Avrami (KJMA) scenario of phase transformation. Specifically the time evolution of the volume fraction of new stable phase is found to follow closely the KJMA formula. By fitting the KJMA formula directly to the simulation data, not only the Avrami exponent but the magnitude of nucleation rate and, in particular, of incubation time are quantitatively studied. The modified Avrami plot is also used to verify the derived KJMA parameters. It is found that the Avrami exponent is close to the ideal theoretical value m =3. The temperature dependence of nucleation rate follows the activation-type behavior expected from the classical nucleation theory. On the other hand, the temperature dependence of incubation time does not follow the exponential activation-type behavior. Rather the incubation time is inversely proportional to the temperature predicted from the theory of Shneidman and Weinberg [J. Non-Cryst. Solids 160, 89 (1993)]. A need to restrict thermal noise in simulation to deduce correct Avrami exponent is also discussed.

Iwamatsu, Masao

2008-02-01

62

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystal and Polytetrahedral-Phase Forming Alloys  

NASA Technical Reports Server (NTRS)

From extensive ground based work on the phase diagram and undercooling studies of Ti-Zr-Ni alloys, have clearly identified the composition of three different phases with progressively increasing polytetrahedral order such as, (Ti/Zr), the C14 Laves phase, and the i-phase, that nucleate directly from the undercooled liquid. The reduced undercooling decreases progressively with increasing polytetrahedral order in the solid, supporting Frank s hypothesis. A new facility for direct measurements of the structures and phase transitions in undercooled liquids (BESL) was developed and has provided direct proof of the primary nucleation of a metastable icosahedral phase in some Ti-Zr-Ni alloys. The first measurements of specific heat and viscosity in the undercooled liquid of this alloy system have been completed. Other than the importance of thermo-physical properties for modeling nucleation and growth processes in these materials, these studies have also revealed some interesting new results (such as a maximum of C(sup q, sub p) in the undercooled state). These ground-based results have clearly established the necessary background and the need for conducting benchmark nucleation experiments at the ISS on this alloy system.

Kelton, K. F.; Gangopadhyay, Anup K.; Lee, G. W.; Hyers, Robert W.; Rathz, T. J.; Robinson, Michael B.; Rogers, Jan R.

2003-01-01

63

Liquid crystal seed nucleates liquid-solid phase change in ceria nanoparticles.  

PubMed

Molecular dynamics (MD) simulation was used to explore the liquid-solid (crystal) phase change of a ceria nanoparticle. The simulations reveal that the crystalline seed, which spontaneously evolves and nucleates crystallisation, is a liquid rather than a solid. Evidence supporting this concept includes: (a) only 3% of the total latent heat of solidification had been liberated after 25% of the nanoparticle had (visibly) crystallised. (b) Cerium ions, comprising the (liquid) crystal seed had the same mobility as cerium ions comprising the amorphous regions. (c) Cerium ion mobility only started to reduce (indicative of solidification) after 25% of the nanoparticle had crystallised. (d) Calculated radial distribution functions (RDF) revealed no long-range structure when 25% of the nanoparticle had (visibly) crystallised. We present evidence that the concept of a liquid crystal seed is more general phenomenon rather than applicable only to nanoceria. PMID:25578038

Sayle, Thi X T; Sayle, Lewis W L; Sayle, Dean C

2015-01-28

64

Ion-induced nucleation in polar one-component fluids  

E-print Network

We present a Ginzburg-Landau theory of ion-induced nucleation in a gas phase of polar one-component fluids, where a liquid droplet grows with an ion at its center. By calculating the density profile around an ion, we show that the solvation free energy is larger in gas than in liquid at the same temperature on the coexistence curve. This difference much reduces the nucleation barrier in a metastable gas.

Hikaru Kitamura; Akira Onuki

2005-08-01

65

Scale-bridging phase-field simulations of microstructure responses on nucleation in metals and colloids  

NASA Astrophysics Data System (ADS)

In the present studies we investigate the connection between atomistic simulation methods, i.e. molecular dynamics (MD) and phase-field crystal (PFC), to the mesoscopic phase-field methods (PFM). While the first describes the evolution of a system on the basis of motion equations of particles the second uses a Cahn-Hilliard type equation to described an atomic density field and the third grounds on the evolution of continuous local order parameter field. The first aim is to point out the ability of the mesoscopic phase-field method to make predictions of growth velocity at the nanoscopic length scale. Therefore the isothermal growth of a spherical crystalline cluster embedded in a melt is considered. We also show simulation techniques that enable to computationally bridge from the atomistic up to the mesoscopic scale. We use a PFM to simulate symmetric thermal dendrites started at an early stage of solidification related to nucleation. These techniques allow to simulate three dimensional dendrites from the state of nuclei (?50 Å) converted from MD up to a size of some ?m where ternary side-arms start to grow.

Berghoff, M.; Nestler, B.

2014-02-01

66

Vapour–to–liquid nucleation: Nucleation theorems for nonisothermal–nonideal case  

SciTech Connect

Homogeneous vapour-to-liquid nucleation, a basic process of aerosol formation, is often considered as a type example of nucleation phenomena, while most treatment of the subject introduce several simplifying assumptions (ideal gas phase, incompressible nucleus, isothermal kinetics, size-independent surface free energy...). During last decades, nucleation theorems have provided new insights into properties of critical nuclei facilitating direct comparison between laboratory experiments and molecular simulations. These theorems are, despite of their generality, often applied in forms where the aforementioned assumptions are made. Here we present forms of nucleation theorems that explicitly take into account these effects and allow direct estimation of their importance. Only assumptions are Arrhenius-type kinetics of nucleation process and exclusion carrier gas molecules from the critical nucleus.

Malila, J.; McGraw, R.; Napari, I.; Laaksonen, A.

2010-08-29

67

Studies of Nucleation, Growth, Specific Heat, and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

Undercooling experiments and thermal physical property measurements of metallic alloys on the International Space Station (ISS) are planned. This recently-funded research focuses on fundamental issues of the formation and structure of highly-ordered non-crystallographic phases (quasicrystals) and related crystal phases (crystal approximants), and the connections between the atomic structures of these phases and those of liquids and glasses. It extends studies made previously by us of the composition dependence of crystal nucleation processes in silicate and metallic glasses, to the case of nucleation from the liquid phase. Motivating results from rf-levitation and drop-tube measurements of the undercooling of Ti/Zr-based liquids that form quasicrystals and crystal approximants are discussed. Preliminary measurements by electrostatic levitation (ESL) are presented.

Kelton, K. F.; Croat, T. K.; Gangopadhyay, A.; Holland-Moritz, D.; Hyers, Robert W.; Rathz, Thomas J.; Robinson, Michael B.; Rogers, Jan R.

2001-01-01

68

Investigating relationships between the seismic "nucleation" phases and breakaway phases of recent Mw 8 earthquakes using global broadband seismic observations  

NASA Astrophysics Data System (ADS)

It is known that the far field P wave velocity observations of large earthquakes frequently start with a small interval of weak motion, which was described as "fore-shock", "pre-shock", or seismic nucleation phase (SNP) by various researchers, e.g, Ellsworth and Beroza (1995). The energetic ground motion immediately following this interesting phase was named as "breakaway" phase. Recent global surveys indicate that for about 50% of Mw>7.5 earthquakes their SNP could be observed teleseismically and the distribution of the earthquakes with SNP appears to be correlated with the tectonic environment and focal mechanisms (Ji et al, 2010; Burkhart and Ji, 2011). Here, a multiple double-couple (MDC) algorithm is developed to quantitatively investigate the relationship between the SNPs and "breakaway" phases of 22 Mw>8 earthquakes since 1990. Our preliminary analysis indicates that the average moment acceleration during the first 4 s of the 2011 Mw 9.1 Tohoku earthquake is only about 2% of that associating with subsequent "breakaway" rupture stage. As the rupture of moderate or large earthquakes often initiate at the vicinity of one of their high slip fault patches, i.e., asperities (Mai et al., 2005), this kind of big discrepancies might shed the light on the intrinsic differences between the asperity and the weak zone in its vicinity, as hypothesized by the asperity theory (e.g., Kanamori, 1981).

Ji, C.

2012-12-01

69

Rate processes in gas phase  

NASA Technical Reports Server (NTRS)

Reaction-rate theory and experiment are given a critical review from the engineers' point of view. Rates of heavy-particle, collision-induced reaction in gas phase are formulated in terms of the cross sections and activation energies for reaction. The effect of cross section function shape and of excited state contributions to reaction both cause the slope of Arrhenius plots to differ from the true activation energy, except at low temperature. The master equations for chemically reacting gases are introduced, and dissociation and ionization reactions are shown to proceed primarily from excited states about kT from the dissociation or ionization limit. Collision-induced vibration, vibration-rotation, and pure rotation transitions are treated, including three-dimensional effects and conservation of energy, which have usually been ignored. The quantum theory of transitions at potential surface crossing is derived, and results are found to be in fair agreement with experiment in spite of some questionable approximations involved.

Hansen, C. F.

1983-01-01

70

5, 51675182, 2005 Gas-phase reaction  

E-print Network

the reactions of NaCl in sea salt particles 5168 #12;ACPD 5, 5167­5182, 2005 Gas-phase reaction of atomicACPD 5, 5167­5182, 2005 Gas-phase reaction of atomic chlorine with aldehydes D. Rodr´iguez et al and Physics Discussions Kinetic study of the gas-phase reaction of atomic chlorine with a series of aldehydes

Paris-Sud XI, Université de

71

Effect of an alpha-phase nucleating agent on the crystallization kinetics of a propylene/ethylene random copolymer at largely different supercooling  

NASA Astrophysics Data System (ADS)

The effect of addition of 0.1 wt% phosphate-ester based alpha-phase nucleating agent on the crystallization of a random propylene-based copolymer with 3.9 mol% ethylene has been investigated by fast scanning chip calorimetry (FSC). Main purpose of the work was the evaluation of the effect of the nucleating agent on the bimodal temperature dependence of the crystallization rate of propylene-based polymers caused by a change of the nucleation mechanism from heterogeneous to homogeneous nucleation on lowering the temperature to below about 60 °C. Presence of the nucleation agent in the copolymer of the present study accelerates crystallization only in the high-temperature range of predominant heterogeneous nucleation, but does not affect the crystallization rate in the low-temperature range of homogeneous nucleation. The observed decrease of the minimum crystallization half-time due to the addition of the nucleation agent, from 0.2 s in case of the unmodified copolymer to 0.04 s in case of the copolymer containing the nucleating agent, is paralleled by an increase of the critical cooling rate required to inhibit crystallization on continuous cooling to below the glass transition temperature from 102 to 103 K s-1. The study is completed by an analysis of the effect of addition of the nucleation agent on the spherulitic superstructure.

Androsch, René; Monami, Andrea; Kucera, Jaroslav

2014-12-01

72

Transient nucleation in glasses  

NASA Technical Reports Server (NTRS)

Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.

Kelton, K. F.

1991-01-01

73

Influence of ferrite nanoparticle type and content on the crystallization kinetics and electroactive phase nucleation of poly(vinylidene fluoride).  

PubMed

This work reports on the nucleation of the ?-phase of poly(vinylidene fluoride) (PVDF) by incorporating CoFe(2)O(4) and NiFe(2)O(4) nanoparticles, leading in this way to the preparation of magnetoelectric composites. The fraction of filler nanoparticles needed to produce the same ?- to ?-phase ratio in crystallized PVDF is 1 order of magnitude lower in the cobalt ferrite nanoparticles. The interaction between nanoparticles and PVDF chains induce the all-trans conformation in PVDF segments, and this structure then propagates in crystal growth. The nucleation kinetics is enhanced by the presence of nanoparticles, as corroborated by the increasing number of spherulites with increasing nanoparticle content and by the variations of the Avrami's exponent. Further, the decrease of the crystalline fraction of PVDF with increasing nanoparticle content indicates that an important fraction of polymer chains are confined in interphases with the filler particle. PMID:21545124

Sencadas, Vitor; Martins, Pedro; Pitães, Alexandre; Benelmekki, Maria; Gómez Ribelles, José Luis; Lanceros-Mendez, Senentxu

2011-06-01

74

A novel image analysis methodology for online monitoring of nucleation and crystal growth during solid state phase transformations.  

PubMed

This study focuses on the development of an automated image analysis method to extract information on nucleation and crystal growth from polarized light micrographs. Using the developed image analysis method, four parameters related to nucleation and crystal growth could be extracted from the images. These parameters were crystalline count (applied as a measure of nucleation), percentage area coverage, average equivalent diameter and average crystalline area (three last parameters applied as a measure for crystal growth). The developed image analysis method was used to investigate two pharmaceutically relevant case studies: first, nitrendipine antisolvent crystallization, and second, recrystallization of amorphous piroxicam solid dispersion in an aqueous environment. In both case studies, an amorphous-to-crystalline phase transformation were observed, which were successfully monitored using real-time Raman spectroscopy. For the both case studies, the parameters related to crystallization kinetics estimated by image analysis were in close agreement with the parameters estimated by Raman spectroscopy. The developed image analysis method proved to be a valuable tool for quantitative monitoring of nucleation and crystal growth with an obvious potential for high throughput screening. PMID:22564780

Wu, Jian X; Xia, Dengning; van den Berg, Frans; Amigo, José Manuel; Rades, Thomas; Yang, Mingshi; Rantanen, Jukka

2012-08-20

75

Nucleation and early stage growth in phase-separating liquid mixtures under weak time-dependent supersaturation  

NASA Astrophysics Data System (ADS)

In the standard description of phase separation, quenching from an initial equilibrium state to a final metastable state in the two-phase region is usually assumed to be instantaneous. Such an artificial situation is nevertheless intrinsically at variance with experiments because the quench rate is finite due to the continuous changes in thermodynamic parameters between the initial and final states. We experimentally explore this issue in near-critical micellar phases of microemulsion with induced transient grating techniques, focusing our attention on the very early stage of droplet growth, where the influence of the time dependence of supersaturation is the strongest. The experiment makes use of laser-induced concentration variations to locally quench the mixture with two intersecting pump beams, whose interference pattern optically traps the nucleated droplets on fringes. Due to the slow mass diffusion kinetics of quenches in composition, the time-resolved reflectivity of a third probe beam on the resulting droplet grating allows us to determine the mean nucleation time and the mean quench depth at the beginning of the decay of the metastable state. By varying the amplitudes of the control parameters (beam power, beam radii), we are able to characterize the dynamic properties of nucleation onset during continuous quenching. The results are interpreted in the light of very simple scaling arguments. We show in particular that R_Cpropto {t_C}^{1/3} for a weak linear temporal variation of the supersaturation, where R_C and t_C are, respectively, the measured critical radius and nucleation time.

Buil, S.; Delville, J. P.; Ducasse, A.

2000-06-01

76

Mechanisms for the deposition of thin metallic films by laser driven gas phase reactions  

SciTech Connect

Gas phase processing makes laser deposition over large areas possible but homogeneous nucleation of large atomic clusters must be avoided if films are to be produced. Clusters can be highly variable in size from a few atoms to significant fractions of a micrometer. If conditions do not allow for complete quenching of the clusters produced in the gas phase, these clusters can arrive at the substrate with sufficient energy to self sinter into homogeneous films which are substantially different from metallic films grown by thermal techniques. Using transmission electron microscopy (TEM), we have characterized the microstructure of thin metallic films deposited by laser breakdown chemical vapor deposition and identified a range of deposition conditions which can lead from powders to homogeneous polycrystalline films and mixed phase materials. Gas phase nucleation is dependent on reactant partial pressures and the gas phase quench rate which can be varied in part by adjusting the H/sub 2/ content of the source gas. Manipulation of these parameters can vary powder size from about one micrometer to less than 2 nanometers. Variation of the quench rate during the deposition of polycrystalline films varies the grain size in the films. Heating the substrate drastically changes the conditions under which the film is formed and as a consequence, can radically alter the microstructure of the film itself. 6 refs., 2 figs.

Jervis, T.R.; Menon, S.K.; Joyce, E.L.; Carroll, D.W.

1986-01-01

77

Phase field models for heterogeneous nucleation: Application to inoculation in alpha-solidifying Ti-Al-B alloys  

NASA Astrophysics Data System (ADS)

This paper aims at briefly reviewing phase field models applied to the simulation of heterogeneous nucleation and subsequent growth, with special emphasis on grain refinement by inoculation. The spherical cap and free growth model (e.g. A.L. Greer, et al., Acta Mater. 48, 2823 (2000)) has proven its applicability for different metallic systems, e.g. Al or Mg based alloys, by computing the grain refinement effect achieved by inoculation of the melt with inert seeding particles. However, recent experiments with peritectic Ti-Al-B alloys revealed that the grain refinement by TiB2 is less effective than predicted by the model. Phase field simulations can be applied to validate the approximations of the spherical cap and free growth model, e.g. by computing explicitly the latent heat release associated with different nucleation and growth scenarios. Here, simulation results for point-shaped nucleation, as well as for partially and completely wetted plate-like seed particles will be discussed with respect to recalescence and impact on grain refinement. It will be shown that particularly for large seeding particles (up to 30 ?m), the free growth morphology clearly deviates from the assumed spherical cap and the initial growth - until the free growth barrier is reached - significantly contributes to the latent heat release and determines the recalescence temperature.

Apel, M.; Eiken, J.; Hecht, U.

2014-02-01

78

Finite-size effects on liquid-solid phase coexistence and the estimation of crystal nucleation barriers.  

PubMed

A fluid in equilibrium in a finite volume V with particle number N at a density ?=N/V exceeding the onset density ?_{f} of freezing may exhibit phase coexistence between a crystalline nucleus and surrounding fluid. Using a method suitable for the estimation of the chemical potential of dense fluids, we obtain the excess free energy due to the surface of the crystalline nucleus. There is neither a need to precisely locate the interface nor to compute the (anisotropic) interfacial tension. As a test case, a soft version of the Asakura-Oosawa model for colloid-polymer mixtures is treated. While our analysis is appropriate for crystal nuclei of arbitrary shape, we find the nucleation barrier to be compatible with a spherical shape and consistent with classical nucleation theory. PMID:25635552

Statt, Antonia; Virnau, Peter; Binder, Kurt

2015-01-16

79

Finite-Size Effects on Liquid-Solid Phase Coexistence and the Estimation of Crystal Nucleation Barriers  

NASA Astrophysics Data System (ADS)

A fluid in equilibrium in a finite volume V with particle number N at a density ? =N /V exceeding the onset density ?f of freezing may exhibit phase coexistence between a crystalline nucleus and surrounding fluid. Using a method suitable for the estimation of the chemical potential of dense fluids, we obtain the excess free energy due to the surface of the crystalline nucleus. There is neither a need to precisely locate the interface nor to compute the (anisotropic) interfacial tension. As a test case, a soft version of the Asakura-Oosawa model for colloid-polymer mixtures is treated. While our analysis is appropriate for crystal nuclei of arbitrary shape, we find the nucleation barrier to be compatible with a spherical shape and consistent with classical nucleation theory.

Statt, Antonia; Virnau, Peter; Binder, Kurt

2015-01-01

80

Gas evolution during water electrolysis  

Microsoft Academic Search

A survey is given of two-phase flow phenomena occurring during boiling and during electrolysis with gas evolution. The analogies and differences between bubble behavior in nucleate boiling and in nucleate electrolysis are discussed. Vapour bubble behavior during nucleate boiling of binary systems is governed by combined heat and mass diffusion. 50 refs.

S. J. D. Van Stralen; C. W. M. P. Sillen

1981-01-01

81

Nucleation of a stable solid from melt in the presence of multiple metastable intermediate phases: wetting, Ostwald's step rule, and vanishing polymorphs.  

PubMed

In many systems, nucleation of a stable solid may occur in the presence of other (often more than one) metastable phases. These may be polymorphic solids or even liquid phases. Sometimes, the metastable phase might have a lower free energy minimum than the liquid but higher than the stable-solid-phase minimum and have characteristics in between the parent liquid and the globally stable solid phase. In such cases, nucleation of the solid phase from the melt may be facilitated by the metastable phase because the latter can "wet" the interface between the parent and the daughter phases, even though there may be no signature of the existence of metastable phase in the thermodynamic properties of the parent liquid and the stable solid phase. Straightforward application of classical nucleation theory (CNT) is flawed here as it overestimates the nucleation barrier because surface tension is overestimated (by neglecting the metastable phases of intermediate order) while the thermodynamic free energy gap between daughter and parent phases remains unchanged. In this work, we discuss a density functional theory (DFT)-based statistical mechanical approach to explore and quantify such facilitation. We construct a simple order-parameter-dependent free energy surface that we then use in DFT to calculate (i) the order parameter profile, (ii) the overall nucleation free energy barrier, and (iii) the surface tension between the parent liquid and the metastable solid and also parent liquid and stable solid phases. The theory indeed finds that the nucleation free energy barrier can decrease significantly in the presence of wetting. This approach can provide a microscopic explanation of the Ostwald step rule and the well-known phenomenon of "disappearing polymorphs" that depends on temperature and other thermodynamic conditions. Theory reveals a diverse scenario for phase transformation kinetics, some of which may be explored via modern nanoscopic synthetic methods. PMID:23713546

Santra, Mantu; Singh, Rakesh S; Bagchi, Biman

2013-10-24

82

Homogeneous vs. heterogeneous nucleation in water-dicarboxylic acid systems  

NASA Astrophysics Data System (ADS)

Binary heterogeneous nucleation of water-succinic/glutaric/malonic/adipic acid on nanometer-sized particles is investigated within the frame of classical heterogeneous nucleation theory. Homogeneous nucleation is also included for comparison. It is found that the nucleation probabilities depend on the contact angle and on the size of the seed particles. New thermodynamical properties, such as saturation vapor pressure, density and surface tension for all the dicarboxylic acid aqueous solutions are included in the calculations. While the new surface tension and density formulations do not bring any significant difference in the computed nucleation rate for homogeneous nucleation for succinic and glutaric acids, the use of the newly derived equations for the vapor pressure decrease the acid concentrations in gas phase by 3 orders of magnitude. According to our calculations, the binary heterogeneous nucleation of succinic acid-water and glutaric acid-water - although it requires a 3-4 orders of magnitude lower vapor concentrations than the homogeneous nucleation - cannot take place under atmospheric conditions. On the other hand binary homogeneous nucleation of adipic acid-water systems might be possible under conditions occuring in upper boundary layer. However, a more detailed characterization of the interaction between the surface and the molecules of the nucleating vapor should be considered in the future.

Hienola, A. I.; Vehkamäki, H.; Riipinen, I.; Kulmala, M.

2009-03-01

83

Homogeneous vs. heterogeneous nucleation in water-dicarboxylic acid systems  

NASA Astrophysics Data System (ADS)

Binary heterogeneous nucleation of water-succinic/glutaric/malonic/adipic acid on nanometer-sized particles is investigated within the frame of classical heterogeneous nucleation theory. Homogeneous nucleation is also included for comparison. It is found that the nucleation probabilities depend on the contact angle and on the size of the seed particles. New thermodynamical properties, such as saturation vapor pressure, density and surface tension for all the dicarboxylic acid aqueous solutions are included in the calculations. While the new surface tension and density formulations do not bring any significant difference in the computed nucleation rate for homogeneous nucleation for succinic and glutaric acids, the use of the newly derived equations for the vapor pressure decrease the acid concentrations in gas phase with 3 orders of magnitude. According to our calculations, the binary heterogeneous nucleation of succinic acid-water and glutaric acid-water although it requires a 3 4 orders of magnitude lower vapor concentrations than the homogeneous nucleation cannot take place in atmospheric conditions. On the other hand binary homogeneous nucleation of adipic acid-water systems might be possible in conditions occuring in upper boundary layer. However, a more detailed characterization of the interaction between the surface and the molecules of the nucleating vapor should be considered in the future.

Hienola, A. I.; Vehkamäki, H.; Riipinen, I.; Kulmala, M.

2008-10-01

84

Probabilistic breakdown phenomenon at on-ramp bottlenecks in three-phase traffic theory: Congestion nucleation in spatially non-homogeneous traffic  

NASA Astrophysics Data System (ADS)

A nucleation model for the breakdown phenomenon in an initial non-homogeneous free traffic flow that occurs at an on-ramp bottleneck is presented. This model is in the context of three-phase traffic theory. In this theory, the breakdown phenomenon is associated with a first-order phase transition from the “free flow” phase to the “synchronized flow” phase. In contrast with many other nucleation models for phase transitions in different systems of statistical physics in which random precluster emergence from fluctuations in an initial homogeneous system foregoes subsequent cluster evolution towards a critical cluster (critical nuclei), random precluster occurrence in free flow at the bottleneck is not necessary for traffic breakdown. In the model, the breakdown phenomenon can also occur if there were no fluctuations in free flow. This is because there is a permanent and motionless non-homogeneity that can be considered a deterministic vehicle cluster localized in a neighborhood of the bottleneck. The presented nucleation model and a nucleation rate of traffic breakdown that follows from the model exhibit qualitatively different features in comparison with previous results. In the nucleation model, traffic breakdown nucleation occurs through a random increase in vehicle number within the deterministic vehicle cluster, if the amplitude of the resulting random vehicle cluster exceeds some critical amplitude. The mean time delay and the associated nucleation rate of traffic breakdown at the bottleneck are found and investigated. The nucleation rate of traffic breakdown as a function of the flow rates to the on-ramp and upstream of the bottleneck is studied. Boundaries for traffic breakdown in the diagram of congested patterns at the bottleneck are found. These boundaries are qualitatively correlated with numerical results of simulation of microscopic traffic flow models in the context of three-phase traffic theory.

Kerner, Boris S.; Klenov, Sergey L.

2006-05-01

85

Simulating and Visualising Phase Transitions: Models for Droplet Nucleation and Growth  

E-print Network

is a famil- iar everyday example. Droplets can be modelled using a field equation such as the Cahn-Hilliard of sizes of clusters present in nucleating systems. Droplet Formation The Cahn-Hilliard model [1, 3] models, the ratio these atoms is known as the mass fraction. In a Cahn-Hilliard system with an extreme mass fraction

Hawick, Ken

86

Nucleation of lamellar domains from a sponge phase under shear flow: Shape selection of nuclei in a nonequilibrium steady state  

NASA Astrophysics Data System (ADS)

It is a fundamental physical problem how a state is selected in a nonequilibrium steady state where the energy is continuously dissipated. This problem is common to phase transitions in liquids under shear flow and those in solids under deformation or electric current. In particular, soft matter often exhibits a strong nonlinear response to an external field, since its structural susceptibility to the external field is extremely large due to its softness and flexibility. Here we study the nucleation and growth process of the lamellar phase from the sponge phase under shear flow in a bilayer-forming surfactant system. We found an interesting shape selection of lamellar nuclei under shear flow between multilamellar vesicles (onions) and cylinders (leeks). These two types of behavior are separated sharply at a critical shear rate: a slight change of the shear rate is enough to switch one behavior to the other. We also found that, under a sufficiently strong shear flow, nucleated onions decrease their size with time, and eventually transform into leeks. This suggests that leeks may be the stable morphology under steady shear flow. However, the stability is limited only to the lamellar-sponge coexistence region. When a system enters into the lamellar phase region by further cooling, leeks lose their stability and break up into rather monodisperse onions, presumably via Rayleigh-like instability of a fluid tube. On the basis of these results, we draw a dynamic state diagram of smectic membrane organization under shear flow.

Miyazawa, Hideyuki; Tanaka, Hajime

2007-07-01

87

Gas-Phase Infrared; JCAMP Format  

National Institute of Standards and Technology Data Gateway

SRD 35 NIST/EPA Gas-Phase Infrared; JCAMP Format (PC database for purchase)   This data collection contains 5,228 infrared spectra in the JCAMP-DX (Joint Committee for Atomic and Molecular Physical Data "Data Exchange") format.

88

Gas-phase pulsed power switches  

Microsoft Academic Search

A review of plasma science that is related to gas-phase pulsed power switching is presented. Switch plasmas include uniform glow-type plasmas and constricted arc-type plasmas, and the science involves understanding transport processes in hydrogen, helium, metal vapor, and other plasmas, and electrode processes including limitations related to cathode emission and sheaths. Gas-phase pulsed power switches include spark gaps, vacuum, metal

Martin A. Gundersen

1991-01-01

89

Bistability in Interstellar Gas-Phase Chemistry  

E-print Network

We present an analysis of "bistability" in gas-phase chemical models of dark interstellar clouds. We identify the chemical mechanisms that allow high- and low-ionization solutions to the chemical rate-equations to coexist. We derive simple analytic scaling relations for the gas densities and ionization rates for which the chemistry becomes bistable. We explain why bistability is sensitive to the H3+ dissociative recombination rate coefficient, and why it is damped by gas-grain neutralization.

Gai I. Boger; Amiel Sternberg

2006-01-16

90

Static mixers with a gas continuous phase  

Microsoft Academic Search

The aim of this work was to characterise hydrodynamics and mass transfer in a gas–liquid contactor containing static mixers (SMs). The originality of this study lies in the fact that these mixing organs are used with a gas continuous phase. Two types of SM were implemented in co-current flows, Statiflo and Lightnin. The pressure drop ?P, the volumic interfacial area

A. Couvert; C. Sanchez; I. Charron; A. Laplanche; C. Renner

2006-01-01

91

Microstructual path analysis of polycrystalline solidification by using multi-phase-field method incorporating a nucleation model  

NASA Astrophysics Data System (ADS)

Using the multi-phase-field (MPF) method incorporating a continuous nucleation model, we have revisited polycrystalline solidification described by the KJMA kinetics. Besides the Avrami exponents, the microstructural path functions to quantify the morphological characteristics were calculated within the framework of the MPF method. Our simulation can easily take account of the effects that are difficult to deduce from the conventional KJMA theory such as grain impingement and spatial distribution of crystallite seeds. As a result, quantitative differences among various types of transformation kinetics can be identified.

Nishida, Yasutaka; Aiga, Fumihiko; Itoh, Satoshi

2014-11-01

92

Project ARGO: Gas phase formation in simulated microgravity  

NASA Technical Reports Server (NTRS)

The ARGO study investigated the reduced incidence of joint pain decompression sickness (DCS) encountered in microgravity as compared with an expected incidence of joint pain DCS experienced by test subjects in Earth-based laboratories (unit gravity) with similar protocols. Individuals who are decompressed from saturated conditions usually acquire joint pain DCS in the lower extremities. Our hypothesis is that the incidence of joint pain DCS can be limited by a significant reduction in the tissue gas micronuclei formed by stress-assisted nucleation. Reductions in dynamic and kinetic stresses in vivo are linked to hypokinetic and adynamic conditions of individuals in zero g. We employed the Doppler ultrasound bubble detection technique in simulated microgravity studies to determine quantitatively the degree of gas phase formation in the upper and lower extremities of test subjects during decompression. We found no evidence of right-to-left shunting through pulmonary vasculature. The volume of gas bubble following decompression was examined and compared with the number following saline contrast injection. From this, we predict a reduced incidence of DCS on orbit, although the incidence of predicted mild DCS still remains larger than that encountered on orbit.

Powell, Michael R.; Waligora, James M.; Norfleet, William T.; Kumar, K. Vasantha

1993-01-01

93

Phase Diagram of a Charged Bose Gas  

Microsoft Academic Search

The phase diagram of a charged Bose gas is drawn. We discuss the domains of existence of the solid, fluid, and superfluid phases. It is predicted that superdense helium can be superfluid at densities higher than 106 g\\/cm3.

J. P. Hansen; B. Jancovici; Daniel Schiff

1972-01-01

94

Nucleation Behavior of Oxygen-Acetylene Torch-Produced Diamond Films  

NASA Technical Reports Server (NTRS)

A mechanism is presented for the nucleation of diamond in the combustion flame environment. A series of six experiments and two associated simulations provide results from which the mechanism was derived. A substantial portion of the prior literature was reviewed and the data and conclusions from the previous experimenters were found to support the proposed mechanism. The nucleation mechanism builds on the work of previous researchers but presents an approach to nucleation in a detail and direction not fully presented heretofore. This work identifies the gas phase as the controlling environment for the initial formation steps leading to nucleation. The developed mechanism explains some of the difficulty which has been found in producing single crystal epitaxial films. An experiment which modified the initial gas phase precursor using methane and carbon monoxide is presented. Addition of methane into the precursor gases was found to be responsible for pillaring of the films. Atomic force microscopy surface roughness data provides a reasonable look at suppression of nucleation by carbon monoxide. Surface finish data was taken on crystals which were open to the nucleation environment and generally parallel to the substrate surface. The test surfaces were measured as an independent measure of the instantaneous nucleation environent. A gas flow and substrate experiment changed the conditions on the surface of the sample by increasing the gas flow rate while remaining on a consistent point of the atomic constituent diagram, and by changing the carbide potential of the substrate. Two tip modification experiments looked at the behavior of gas phase nucleation by modifying the shape and behavior of the flame plasma in which the diamond nucleation is suspected to occur. Diamond nucleation and growth was additionally examined using a high-velocity oxygen fuel gun and C3H6 as the fuel gas phase precursor with addition of carbon monoxide gas 01 addition of liquid toluene.

Roberts, F. E.

2003-01-01

95

Cryogenic two-phase flow during chilldown: Flow transition and nucleate boiling heat transfer  

NASA Astrophysics Data System (ADS)

The recent interest in space exploration has placed a renewed focus on rocket propulsion technology. Cryogenic propellants are the preferred fuel for rocket propulsion since they are more energetic and environmentally friendly compared with other storable fuels. Voracious evaporation occurs while transferring these fluids through a pipeline that is initially in thermal equilibrium with the environment. This phenomenon is referred to as line chilldown. Large temperature differences, rapid transients, pressure fluctuations and the transition from the film boiling to the nucleate boiling regime characterize the chilldown process. Although the existence of the chilldown phenomenon has been known for decades, the process is not well understood. Attempts have been made to model the chilldown process; however the results have been fair at best. A major shortcoming of these models is the use of correlations that were developed for steady, non-cryogenic flows. The development of reliable correlations for cryogenic chilldown has been hindered by the lack of experimental data. An experimental facility was constructed that allows the flow structure, the temperature history and the pressure history to be recorded during the line chilldown process. The temperature history is then utilized in conjunction with an inverse heat conduction procedure that was developed, which allows the unsteady heat transfer coefficient on the interior of the pipe wall to be extracted. This database is used to evaluate present predictive models and correlations for flow regime transition and nucleate boiling heat transfer. It is found that by calibrating the transition between the stratified-wavy and the intermittent/annular regimes of the Taitel and Dukler flow regime map, satisfactory predictions are obtained. It is also found that by utilizing a simple model that includes the effect of flow structure and incorporating the enhancement provided by the local heat flux, significant improvement in the predictive capabilities of the Muller-Steinhagen and Jamialahmadi correlation for nucleate flow boiling is achieved.

Jackson, Jelliffe Kevin

96

Sublimating comets as the source of nucleation seeds for grain condensation in the gas outflow from AGB stars  

NASA Technical Reports Server (NTRS)

A growing amount of observational and theoretical evidence suggests that most main sequence stars are surrounded by disks of cometary material. The dust production by comets in such disks is investigated when the central stars evolve up the red giant and asymptotic giant branch (AGB). Once released, the dust is ablated and accelerated by the gas outflow and the fragments become the seeds necessary for condensation of the gas. The origin of the requisite seeds has presented a well known problem for classical nucleation theory. This model is consistent with the dust production observed in M giants and supergiants (which have increasing luminosities) and the fact that earlier supergiants and most WR stars (whose luminosities are unchanging) do not have significant dust clouds even though they have significant stellar winds. Another consequence of the model is that the spatial distribution of the dust does not, in general, coincide with that of the gas outflow, in contrast to the conventional condensation model. A further prediction is that the condensation radius is greater that that predicted by conventional theory which is in agreement with IR interferometry measurements of alpha-Ori.

Whitmire, D. P.; Matese, John J.; Reynolds, R. T.

1989-01-01

97

Gas Accretion by Globular Clusters and Nucleated Dwarf Galaxies and the Formation of the Arches and Quintuplet Clusters  

E-print Network

We consider here the collective accretion of gas by globular clusters and dwarf galaxies moving through the interstellar medium. In the limit of high velocity and/or sound speed of the ISM, the collective potential of the cluster is insufficient to accrete significant amounts of gas, and stars within the systems accrete gas individually. We show, however, that when the sound speed or the relative velocity of the ambient medium is less than the central velocity dispersion of the cluster, it is accreted into the collective potential of the cluster prior to being accreted onto the individual stars within the cluster. The collective rate is strongly enhanced relative to the individual rates. This effect may potentially modify the white dwarf cooling sequence in globular clusters with low-inclination and low-eccentricity Galactic orbits, and lead to the rejuvenation of some marginally surviving cores of globular clusters and nucleated dwarf galaxies near the Galactic center. Such effects will only occur rarely, but may explain the existence of clusters of young, massive stars near the Galactic center.

Douglas N. C. Lin; Stephen D. Murray

2007-03-30

98

Probabilistic breakdown phenomenon at on-ramp bottlenecks in three-phase traffic theory: Congestion nucleation in spatially non-homogeneous traffic  

Microsoft Academic Search

A nucleation model for the breakdown phenomenon in an initial non-homogeneous free traffic flow that occurs at an on-ramp bottleneck is presented. This model is in the context of three-phase traffic theory. In this theory, the breakdown phenomenon is associated with a first-order phase transition from the ``free flow'' phase to the ``synchronized flow'' phase. In contrast with many other

Boris S. Kerner; Sergey L. Klenov

2006-01-01

99

Probabilistic breakdown phenomenon at on-ramp bottlenecks in three-phase traffic theory: Congestion nucleation in spatially non-homogeneous traffic  

Microsoft Academic Search

A nucleation model for the breakdown phenomenon in an initial non-homogeneous free traffic flow that occurs at an on-ramp bottleneck is presented. This model is in the context of three-phase traffic theory. In this theory, the breakdown phenomenon is associated with a first-order phase transition from the “free flow” phase to the “synchronized flow” phase. In contrast with many other

Boris S. Kerner; Sergey L. Klenov

2006-01-01

100

Large area diamond nucleation on Si(001) using magnetoactive microwave plasma CVD  

NASA Astrophysics Data System (ADS)

Uniform diamond nucleation was succeeded on Si(001) substrate over a large area (3 cm × 4 cm) by magnetoactive microwave plasma CVD. CH4/He gas mixture was used as source gas in order to obtain high radical density in the nucleation step. The effect of substrate bias voltage on the nucleation was examined. The results show that a suitable positive bias voltage applied to the substrate can enhance diamond nucleation while negative bias voltages lead to the deposition of only non-diamond phase carbon. The CH 3 radical density was measured using infrared laser absorption spectroscopy in order to investigate the effect of radical species on the nucleation. The results are discussed in relation to the important factors on the bias-enhanced diamond nucleation.

Jeon, Hyeongmin; Hatta, Akimitsu; Suzuki, Hidetoshi; Ito, Toshimichi; Sasaki, Takatomo; Lee, Chongmu; Hiraki, Akio

1997-04-01

101

Heterogeneous nucleation of a monomer gas on a growing gas-phase polymer  

E-print Network

-chain polymer. Reiss and co-workers have shown that cloud chambers can be extraordinarily sensitive detectors, and isoprene could be studied in molecular detail through the use of a diffusion cloud chamber or an expansion cloud chamber as a detector. The central physical idea of these experiments is that when a polymer grows

Seok, Chaok

102

Initial nucleation site formation due to acoustic droplet vaporization  

PubMed Central

Acoustic droplet vaporization (ADV) is the selective vaporization of liquid microdroplets using ultrasound, resulting in gas bubbles. The ADV process has been proposed as a tool in biomedical applications such as gas embolotherapy, drug delivery, and phase-change contrast agents. Using a 7.5?MHz focused transducer, the initial gas nucleus formed in perfluorocarbon microdroplets was directly visualized using ultra-high speed imaging. The experimental results of initial nucleation site location were compared to a 2D axisymmetric linear acoustic model investigating the focal spot of the acoustic wave within the microdroplets. Results suggest a wavelength to droplet diameter dependence on nucleation site formation. PMID:24711671

Li, David S.; Kripfgans, Oliver D.; Fabiilli, Mario L.; Brian Fowlkes, J.; Bull, Joseph L.

2014-01-01

103

Tetragonal Lysozyme Nucleation and Crystal Growth: The Role of the Solution Phase  

NASA Technical Reports Server (NTRS)

Lysozyme, and most particularly the tetragonal form of the protein, has become the default standard protein for use in macromolecule crystal nucleation and growth studies. There is a substantial body of experimental evidence, from this and other laboratories, that strongly suggests this proteins crystal nucleation and growth is by addition of associated species that are preformed by standard reversible concentration-driven self association processes in the bulk solution. The evidence includes high resolution AFM studies of the surface packing and of growth unit size at incorporation, fluorescence resonance energy transfer measurements of intermolecular distances in dilute solution, dialysis kinetics, and modeling of the growth rate data. We have developed a selfassociation model for the proteins crystal nucleation and growth. The model accounts for the obtained crystal symmetry, explains the observed surface structures, and shows the importance of the symmetry obtained by self-association in solution to the process as a whole. Further, it indicates that nucleation and crystal growth are not distinct mechanistically, but identical, with the primary difference being the probability that the particle will continue to grow or dissolve. This model also offers a possible mechanism for fluid flow effects on the growth process and how microgravity may affect it. While a single lysozyme molecule is relatively small (M.W. = 14,400), a structured octamer in the 4(sub 3) helix configuration (the proposed average sized growth unit) would have a M.W. = 115,000 and dimensions of 5.6 x 5.6 x 7.6 nm. Direct AFM measurements of growth unit incorporation indicate that units as wide as 11.2 nm and as long as 11.4 nm commonly attach to the crystal. These measurements were made at approximately saturation conditions, and they reflect the sizes of species that both added or desorbed from the crystal surface. The larger and less isotropic the associated species the more likely that it will be oriented to some degree in a flowing boundary layer, even at the low flow velocities measured about macromolecule crystals. Flow-driven effects resulting in misorientation upon addition to and incorporation into the crystal need only be a small fraction of a percentage to significantly affect the resulting crystal. One Earth, concentration gradient driven flow will maintain a high interfacial concentration, i.e., a high level (essentially that of the bulk solution) of solute association at the interface and higher growth rate. Higher growth rates mean an increased probability that misaligned growth units are trapped by subsequent growth layers before they can be desorbed and try again, or that the desorbing species will be smaller than the adsorbing species. In microgravity the extended diffusive boundary layer will lower the interfacial concentration. This results in a net dissociation of aggregated species that diffuse in from the bulk solution, i.e., smaller associated species, which are more likely able to make multiple attempts to correctly bind, yielding higher quality crystals.

Pusey, Marc L.; Forsythe, Elizabeth; Sumida, John; Maxwell, Daniel; Gorti, Sridhar

2002-01-01

104

EPA GAS PHASE CHEMISTRY CHAMBER STUDIES  

EPA Science Inventory

Gas-phase smog chamber experiments are being performed at EPA in order to evaluate a number of current chemical mechanisms for inclusion in EPA regulatory and research models. The smog chambers are 9000 L in volume and constructed of 2-mil teflon film. One of the chambers is co...

105

Characterization of Soot Deposition and Particle Nucleation in Exhaust Gas Recirculation Coolers  

Microsoft Academic Search

Cooled exhaust gas recirculation (EGR) is used to control engine out NOx (oxides of nitrogen) emissions from modern diesel engines by re-circulating a portion of the exhaust gases into the intake manifold of an engine after cooling it through a heat exchanger commonly referred to as an EGR cooler. However, EGR cooler fouling due to presence of soot particles and

Anil Singh Bika; Alok Warey; David Long; Sandro Balestrino; Patrick Szymkowicz

2012-01-01

106

From gas-phase oxidation of SO2 by SO4- to the formation of sulfuric acid  

NASA Astrophysics Data System (ADS)

One of the difficulties to predict atmospheric nucleation is related to inaccurate measure of the total sulfuric acid concentration. We present a density functional theory investigation of the SO2 gas phase oxidation by SO4-. In the immediate product, SO2.SO4- cluster, SO2 is subsequently oxidized and SO3SO3- is formed at 1.7 × 10-7 s-1 reaction rate. SO3SO3- interacts with O2 molecule to form SO3 and SO5-, which are important species in the gas phase chemistry of sulfur and in the formation mechanism of sulfuric acid.

Tsona, Narcisse; Bork, Nicolai; Vehkamäki, Hanna

2013-05-01

107

Gas-phase electron diffraction studies of unstable molecules   

E-print Network

Gas-phase electron diffraction (GED) is the only viable technique for the accurate structural study of gas-phase molecules that contain more than ~10 atoms. Recent advances in Edinburgh have made it possible to study ...

Noble-Eddy, Robert

2009-01-01

108

Gas-Phase Photoionization Of A Protein  

NASA Astrophysics Data System (ADS)

We present preliminary results on gas phase photoionization of electrosprayproduced multiply protonated cytochrome c protein (104 amino acids; Ë?12.4 kDa), which has been achieved with a newly developed experimental system for spectroscopy of electrosprayed ions in a linear quadrupole ion trap using a monochromatized vacuum ultraviolet (VUV) synchrotron radiation and tandem mass spectrometry method. The investigation of proteins in the gas phase, where they are free of the influence of counterions and solvent molecules, offer a possibility to understand their intrinsic molecular properties. However, due to limited both ion densities and available number of photons, the use of synchrotron radiation for the trapped ions spectroscopy is a rather challenging task. The feasibility of coupling a Fourier transform ion cyclotron resonance ion trap with soft x-ray synchrotron beamline and the first successful use of synchrotron radiation for spectroscopy of electrosprayed negative ions stored in a three-dimensional quadrupole ion trap have been demonstrated only recently (R. Thissen et al., 2008, Phys. Rev. Lett., 100, 223001; A. Giulliani et al., Proc. 57th ASMS Conf., Philadelphia, 2009). The present results are the first reported on photoionization of kDa species in the gas phase and are valuable regarding both a fundamental interest of accessing physical properties of large biological ions isolated in vacuo and potential development of a new technique for proteomics.

Milosavljevic, A. R.; Giuliani, A.; Nicolas, C.; Gil, J.-F.; Lemaire, J.; Refregiers, M.; Nahon, L.

2010-07-01

109

In-plane bidimensional stripes in thin films of CCH-PCH mixtures: possible nucleation of a tilted smectic phase  

NASA Astrophysics Data System (ADS)

Spontaneous in-plane bidimensional stripes are predicted to appear in thin films of tilted smectic liquid crystals, due to flexopolarization, provided the flexoelectric coefficients are great enough, as in several smectic C's. The two periodicities arise in orthogonal directions. In the presence of free ions, the charge distributions becomes also modulated in-plane, partially masking the direct flexopolarization influence. Both effective periods are of the order of 10 micrometers . The optical observations were performed on mixtures of trans-4-(trans-4'-n- amylcyclohexyl) cyclohexanecarboxylic acid (CCH) and of 4-(trans-4'-n-amylcyclohexyl) benzoic acid (PCH). Both pure compounds exhibit only a nematic phase, the first between 224 degree(s)C and 243 degree(s)C, and the second one between 180 degree(s)C and 265 degree(s)C. The experimental data are consistent with the present model, suggesting that, for certain CCH/PCH ratios less than 30%, a tilted smectic phase is nucleated close to the melting point.

Pikin, Sergei A.; Torgova, Sofia I.; Strigazzi, Alfredo

1996-01-01

110

Fuel Performance Experiments and Modeling: Fission Gas Bubble Nucleation and Growth in Alloy Nuclear Fuels  

SciTech Connect

Advanced fast reactor systems being developed under the DOE's Advanced Fuel Cycle Initiative are designed to destroy TRU isotopes generated in existing and future nuclear energy systems. Over the past 40 years, multiple experiments and demonstrations have been completed using U-Zr, U-Pu-Zr, U-Mo and other metal alloys. As a result, multiple empirical and semi-empirical relationships have been established to develop empirical performance modeling codes. many mechamistic questions about fission as mobility, bubble coalescience, and gas release have been answered through industrial experience, reearch, and empirical understanding. The advent of modern computational materials science, however, opens new doors of development such that physics-based multi-scale models may be developed to enable a new generation of predictive fuel performance codes that are not limited by empiricism.

McDeavitt, Sean; Shao, Lin; Tsvetkov, Pavel; Wirth, Brian; Kennedy, Rory

2014-04-07

111

Homogeneous nucleation kinetics  

NASA Technical Reports Server (NTRS)

Homogeneous nucleation kinetics are rederived in a manner fundamentally similar to the approach of classical nucleation theory with the following modifications and improvements. First, the cluster is a parent phase cluster and does not require energization to the parent state. Second, the thermodynamic potential used to describe phase stability is a continuous function along the pathway of phase decomposition. Third, the kinetics of clustering corresponds directly to the diffusional flux of monomers through the cluster distribution and are formally similar to classical theory with the resulting kinetic equation modified by two terms in the preexponential factor. These terms correct for the influence of a supersaturation dependent clustering within the parent phase and for the influence of an asymmetrical cluster concentration as a function of cluster size at the critical cluster size. Fourth, the supersaturation dependence of the nucleation rate is of the same form as that given by classical nucleation theory. This supersaturation dependence must however be interpreted in terms of a size dependent surface tension. Finally, there are two scaling laws which describe supersaturation to either constant nucleation rate or to the thermodynamically determined physical spinodal.

Rasmussen, D. H.; Appleby, M. R.; Leedom, G. L.; Babu, S. V.; Naumann, R. J.

1983-01-01

112

Initiation of the ice phase by marine biogenic surfaces in supersaturated gas and supercooled aqueous phases.  

PubMed

Biogenic particles have the potential to affect the formation of ice crystals in the atmosphere with subsequent consequences for the hydrological cycle and climate. We present laboratory observations of heterogeneous ice nucleation in immersion and deposition modes under atmospherically relevant conditions initiated by Nannochloris atomus and Emiliania huxleyi, marine phytoplankton with structurally and chemically distinct cell walls. Temperatures at which freezing, melting, and water uptake occur are observed using optical microscopy. The intact and fragmented unarmoured cells of N. atomus in aqueous NaCl droplets enhance ice nucleation by 10-20 K over the homogeneous freezing limit and can be described by a modified water activity based ice nucleation approach. E. huxleyi cells covered by calcite plates do not enhance droplet freezing temperatures. Both species nucleate ice in the deposition mode at an ice saturation ratio, S(ice), as low as ~1.2 and below 240 K, however, for each, different nucleation modes occur at warmer temperatures. These observations show that markedly different biogenic surfaces have both comparable and contrasting effects on ice nucleation behaviour depending on the presence of the aqueous phase and the extent of supercooling and water vapour supersaturation. We derive heterogeneous ice nucleation rate coefficients, J(het), and cumulative ice nuclei spectra, K, for quantification and analysis using time-dependent and time-independent approaches, respectively. Contact angles, ?, derived from J(het)via immersion freezing depend on T, a(w), and S(ice). For deposition freezing, ? can be described as a function of S(ice) only. The different approaches yield different predictions of atmospheric ice crystal numbers primarily due to the time evolution allowed for the time-dependent approach with implications for the evolution of mixed-phase and ice clouds. PMID:21912788

Alpert, Peter A; Aller, Josephine Y; Knopf, Daniel A

2011-11-28

113

On the nucleation and propagation of phase transformation fronts in a NiTi alloy  

Microsoft Academic Search

In this paper we present an experimental methodology for simultaneous full field monitoring of the deformation and thermal changes in NiTi during mechanically unstable regimes associated with the pseudoelastic material response. The deformation history is established by photographically recording surface changes of a brittle coating as austenite-martensite phase transition fronts traverse the specimen. Temperature changes are monitored by infrared thermal

J. A. Shaw; S. Kyriakides

1997-01-01

114

Carbon phases versus hydrogen phases: neutral gas in nearby galaxies  

NASA Astrophysics Data System (ADS)

Due to its lower-than-hydrogen first ionization energy, atomic carbon is ionized throughout the diffuse ISM, tracing both regions of ioinized and neutral hydrogen gas. On the other hand, carbon monoxide (CO) exists and emits exclusively where hydrogen is in molecular form. Neutral atomic carbon is predicted to exist in between these phases, but recent evidence in our Galaxy and from simulations show it may be closely tied to the molecular gas than previously thought. Here, we investigate the gas in various carbon stages (evidenced through emission in [CII], [CI] and CO) compared to hydrogen stages (through ?CO-corrected CO for H2 and HI emission). The observations are based upon the Beyond the Peak sample of 22 galaxies with data from the Herschel Space Observatory SPIRE FTS instrument, as well as relying on ground-based CO and HI observations. Based on these comparisons, [CI] does trace CO well and thus may provide a good way to trace molecular gas in external galaxies as well as in molecular clouds in the Milky Way.

Crocker, Alison Faye; Pellegrini, Eric; Smith, John-David T.; Beyond the Peak Team

2015-01-01

115

Substrate-free gas-phase synthesis of graphene  

NASA Astrophysics Data System (ADS)

Graphene is a single atomic layer of sp2-bonded carbon atoms tightly packed in a two-dimensional honeycomb lattice. The material possesses remarkable properties and has been envisioned for use in numerous applications. Contemporary graphene production techniques require substrates or graphite crystals to create graphene. Furthermore, these approaches involve multiple steps, and sometimes non-ambient conditions, to produce atomically-thin sheets. This dissertation presents the first substrate-free gas-phase graphene synthesis method. The technique can synthesize graphene in a single step at atmospheric pressure, without the use of graphite or substrates. The novel synthesis method was discovered through experiments that tested the hypothesis that graphene could be synthesized through the delivery of alcohols into argon plasmas. The experiments presented in this dissertation were conducted in an atmospheric-pressure microwave plasma reactor. Solid carbon materials were produced by delivering liquid ethanol droplets directly into argon plasmas. Numerous characterization techniques were used to unambiguously prove that the synthesized materials were clean and highly ordered graphene sheets. Additional studies investigated the effects of variable experimental parameters on the graphene synthesis process. The applied microwave power did not significantly affect the types of structures produced in the reactor. Lowering the volumetric flow rate of the plasma gas resulted in the synthesis of graphitic particles. The composition of the precursors delivered into the reactor also affected graphene synthesis. Graphene was not produced through the delivery of methanol or isopropyl alcohol droplets. However, graphene was obtained through dimethyl ether, which is an organic compound with the same atomic composition as ethanol. Thus, the flow rate and precursor composition significantly affected the nucleation, growth, and residence time of the materials created during experiments. A practical application for the synthesized graphene is also presented in this dissertation. The sheets were found to be an ideal support structure for the transmission electron microscopy characterization of nanoparticles coated with molecular layers. The substrate-free gas-phase method is capable of rapid and continuous graphene synthesis at ambient pressure. The simplicity of the approach makes it scalable for industrial graphene production. The novel technique presented in this dissertation could substantially enable graphene research and applications.

Dato, Albert Manglallan

116

Polymorphic phase transition among the titania crystal structures using a solution-based approach: from precursor chemistry to nucleation process.  

PubMed

Nanocrystalline titania are a robust candidate for various functional applications owing to its non-toxicity, cheap availability, ease of preparation and exceptional photochemical as well as thermal stability. The uniqueness in each lattice structure of titania leads to multifaceted physico-chemical and opto-electronic properties, which yield different functionalities and thus influence their performances in various green energy applications. The high temperature treatment for crystallizing titania triggers inevitable particle growth and the destruction of delicate nanostructural features. Thus, the preparation of crystalline titania with tunable phase/particle size/morphology at low to moderate temperatures using a solution-based approach has paved the way for further exciting areas of research. In this focused review, titania synthesis from hydrothermal/solvothermal method, conventional sol-gel method and sol-gel-assisted method via ultrasonication, photoillumination and ILs, thermolysis and microemulsion routes are discussed. These wet chemical methods have broader visibility, since multiple reaction parameters, such as precursor chemistry, surfactants, chelating agents, solvents, mineralizer, pH of the solution, aging time, reaction temperature/time, inorganic electrolytes, can be easily manipulated to tune the final physical structure. This review sheds light on the stabilization/phase transformation pathways of titania polymorphs like anatase, rutile, brookite and TiO2(B) under a variety of reaction conditions. The driving force for crystallization arising from complex species in solution coupled with pH of the solution and ion species facilitating the orientation of octahedral resulting in a crystalline phase are reviewed in detail. In addition to titanium halide/alkoxide, the nucleation of titania from other precursors like peroxo and layered titanates are also discussed. The non-aqueous route and ball milling-induced titania transformation is briefly outlined; moreover, the lacunae in understanding the concepts and future prospects in this exciting field are suggested. PMID:24969423

Kumar, S Girish; Rao, K S R Koteswara

2014-10-21

117

Polymorphic phase transition among the titania crystal structures using a solution-based approach: from precursor chemistry to nucleation process  

NASA Astrophysics Data System (ADS)

Nanocrystalline titania are a robust candidate for various functional applications owing to its non-toxicity, cheap availability, ease of preparation and exceptional photochemical as well as thermal stability. The uniqueness in each lattice structure of titania leads to multifaceted physico-chemical and opto-electronic properties, which yield different functionalities and thus influence their performances in various green energy applications. The high temperature treatment for crystallizing titania triggers inevitable particle growth and the destruction of delicate nanostructural features. Thus, the preparation of crystalline titania with tunable phase/particle size/morphology at low to moderate temperatures using a solution-based approach has paved the way for further exciting areas of research. In this focused review, titania synthesis from hydrothermal/solvothermal method, conventional sol-gel method and sol-gel-assisted method via ultrasonication, photoillumination and ILs, thermolysis and microemulsion routes are discussed. These wet chemical methods have broader visibility, since multiple reaction parameters, such as precursor chemistry, surfactants, chelating agents, solvents, mineralizer, pH of the solution, aging time, reaction temperature/time, inorganic electrolytes, can be easily manipulated to tune the final physical structure. This review sheds light on the stabilization/phase transformation pathways of titania polymorphs like anatase, rutile, brookite and TiO2(B) under a variety of reaction conditions. The driving force for crystallization arising from complex species in solution coupled with pH of the solution and ion species facilitating the orientation of octahedral resulting in a crystalline phase are reviewed in detail. In addition to titanium halide/alkoxide, the nucleation of titania from other precursors like peroxo and layered titanates are also discussed. The non-aqueous route and ball milling-induced titania transformation is briefly outlined; moreover, the lacunae in understanding the concepts and future prospects in this exciting field are suggested.

Kumar, S. Girish; Rao, K. S. R. Koteswara

2014-09-01

118

Gas phase thermochemistry of organogermanium compounds  

SciTech Connect

A variety of silyl- and alkyl-germylene precursors have been synthesized and subsequently pyrolyzed in the gas phase. Arrhenius parameters were obtained employing a pulsed-stirred flow reactor for these unimolecular decompositions. These precursors are divided into two major categories by mechanism of germylene extrusion: {alpha}-elimination precursors and germylacetylenes. The extrusion of germylenes from germylacetylene precursors is of primary interest. A mechanism is proposed employing a germacyclopropene intermediate. Evidence supporting this mechanism is presented. In the process of exploring germylacetylenes as germylene precursors, an apparent dyatropic rearrangement between germanium and silicon was observed. This rearrangement was subsequently explored.

Engel, J.P.

1993-12-07

119

Photoinduced gas-phase electron transfer reactions.  

PubMed

The electron transfer quenching process, when a reactive excited state is singlet or triplet, for gas-phase systems (benzophenone and anthraquinone with amines and pyridine as well as carbazole with halomethanes) was systematically investigated using time-resolved fluorescence. Bimolecular rate constants were obtained. Variable-temperature measurements were performed for eight donor-acceptor pairs. It was found that under solvent-free conditions various quenchers differing in photochemical reactivity led to change in quenching rates by almost three orders of magnitude. Positive and negative temperature dependences for the electron transfer rate constants were observed. The data were analyzed in terms of the Marcus-Jortner theory. PMID:15615042

Zalesskaya, G A; Sambor, E G; Bely, N N

2004-03-01

120

Gas-phase photolysis of tungsten hexachloride  

NASA Astrophysics Data System (ADS)

The laser-induced decomposition of WCl6 in the gas-phase is investigated by means of absorption, Raman and laser-induced fluorescence spectroscopy. With visible Ar+-laser radiation dissociation of WCl6 into WCl4 and Cl2 has been observed. Further decomposition can be achieved in the presence of H2 employing ultraviolet Ar+-laser radiation at 360 nm. A complete reduction to W requires even shorter wavelengths. The experimental results are analyzed on the basis of model calculations. Implications on the Laser-induced Chemical Vapor Deposition (LCVD) of W are discussed.

Kullmer, R.

1994-07-01

121

Giddings Austin chalk enters deep lean-gas phase  

SciTech Connect

Deep lean gas is the latest phase in the growth of the Giddings field Austin chalk play. The first phase involved drilling vertical oil and gas wells. Next came the horizontal well boom in the shallower Austin chalk area, which is still continuing. And now this third phase places horizontal laterals in the Austen chalk at about 14,000--15,000 ft to produce lean gas. The article describes the producing wells and gas gathering.

Moritis, G.

1995-12-25

122

Vaccum Gas Tungsten Arc Welding, phase 1  

NASA Technical Reports Server (NTRS)

This two year program will investigate Vacuum Gas Tungsten Arc Welding (VGTAW) as a method to modify or improve the weldability of normally difficult-to-weld materials. VGTAW appears to offer a significant improvement in weldability because of the clean environment and lower heat input needed. The overall objective of the program is to develop the VGTAW technology and implement it into a manufacturing environment that will result in lower cost, better quality and higher reliability aerospace components for the space shuttle and other NASA space systems. Phase 1 of this program was aimed at demonstrating the process's ability to weld normally difficult-to-weld materials. Phase 2 will focus on further evaluation, a hardware demonstration and a plan to implement VGTAW technology into a manufacturing environment. During Phase 1, the following tasks were performed: (1) Task 11000 Facility Modification - an existing vacuum chamber was modified and adapted to a GTAW power supply; (2) Task 12000 Materials Selection - four difficult-to-weld materials typically used in the construction of aerospace hardware were chosen for study; (3) Task 13000 VGTAW Experiments - welding experiments were conducted under vacuum using the hollow tungsten electrode and evaluation. As a result of this effort, two materials, NARloy Z and Incoloy 903, were downselected for further characterization in Phase 2; and (4) Task 13100 Aluminum-Lithium Weld Studies - this task was added to the original work statement to investigate the effects of vacuum welding and weld pool vibration on aluminum-lithium alloys.

Weeks, J. L.; Krotz, P. D.; Todd, D. T.; Liaw, Y. K.

1995-01-01

123

Infrared Spectroscopy of Gas Phase Metal Clusters  

NASA Astrophysics Data System (ADS)

The combination of its various performance characteristics make the free electron laser FELIX ideally suited to resonantly pump large amounts of vibrational energy into isolated gas-phase species. This energy can then subsequently trigger reactions, it can lead to the emission of photons (fluorescence), to the release of fragments (dissociation) or to the ejection of electrons (ionization). By monitoring these IR laser induced processes as a function of excitation wavelength, IR spectroscopic information, can be obtained. In one experiment, FELIX is used to excite strongly bound gas-phase clusters to levels that are high enough to enable the thermal emission of an electron. When the (mass selected) ion yield is monitored as a function of wavelength, IR spectra of the clusters can be obtained. This IR laser induced ionization has been found to work very efficiently for clusters that are strongly bound and that have comparatively low ionization potentials. The spectra of various metal-carbide, -oxide and -nitride clusters have been measured and the analysis of these spectra as a function of size of the cluster yields information on the cluster structure and on its evolution from small systems to the bulk limit.

van Heijnsbergen, Deniz; Meijer, Gerard; Duncan, Michael; von Helden, Gert

2002-03-01

124

The strong influence of internal stresses on the nucleation of a nanosized, deeply undercooled melt at a solid-solid phase interface.  

PubMed

The effect of elastic energy on nucleation and disappearance of a nanometer size intermediate melt (IM) region at a solid-solid (S1S2) phase interface at temperatures 120 K below the melting temperature is studied using a phase-field approach. Results are obtained for broad range of the ratios of S1S2 to solid-melt interface energies, kE, and widths, k?. It is found that internal stresses only slightly promote barrierless IM nucleation but qualitatively alter the system behavior, allowing for the appearance of the IM when kE < 2 (thermodynamically impossible without mechanics) and elimination of what we termed the IM-free gap. Remarkably, when mechanics is included within this framework, there is a drastic (16 times for HMX energetic crystals) reduction in the activation energy of IM critical nucleus. After this inclusion, a kinetic nucleation criterion is met, and thermally activated melting occurs under conditions consistent with experiments for HMX, elucidating what had been to date mysterious behavior. Similar effects are expected to occur for other material systems where S1S2 phase transformations via IM take place, including electronic, geological, pharmaceutical, ferroelectric, colloidal, and superhard materials. PMID:25789667

Momeni, Kasra; Levitas, Valery I; Warren, James A

2015-04-01

125

Nucleation of cubic GaN/GaAs (001) grown by gas source molecular beam epitaxy with hydrazine  

NASA Astrophysics Data System (ADS)

Growth nucleation and evolution of morphology of GaN on (001) GaAs is investigated as a function of the N2H4/Ga flux ratio. The use of hydrazine allows us to reach high flux ratios without causing any damage to the epitaxial layer. Epitaxial GaN is purely cubic but shows growth anisotropy dependent on the flux ratio. GaN layers grown at low flux ratios show three-dimensional nucleation and no preferential island orientation. With higher flux ratios, the nucleation rate increases, the surface becomes smoother, and the growth anisotropy markedly increases. The growth morphology reflects the surface anisotropy of the underlying GaAs substrate.

Nikishin, S. A.; Antipov, V. G.; Ruvimov, S. S.; Seryogin, G. A.; Temkin, H.

1996-11-01

126

Dependence of nucleation rates on sulfuric acid vapor concentration in PoValley, Italy  

NASA Astrophysics Data System (ADS)

A field campaign was conducted at the polluted rural site, San Pietro Capofiume (SPC) in PoValley, Italy, from June 26th to July 12th 2009 in the framework of the EUCAARI (European integrated project on aerosol, cloud, climate, and air interactions) project. The gas-phase sulfuric acid concentrations were measured for the first time at SPC station during this campaign. Here we examine the dependence of nucleation rate on sulfuric acid vapor concentrations in SPC. The apparent nucleation rate - i.e. formation rate of 3 nm particles - was directly determined from differential mobility particle sizer data. The nucleation rate at 1 nm (J1) was then calculated by accounting for the coagulation of the sub-3 nm clusters with large particles during their growth from 1 to 3 nm. The dependence of J1 on [H2SO4] was studied for each nucleation day individually and for all nucleation days as a whole. It is usually assumed that the dependence of nucleation rate on sulfuric acid concentration follows a simple power law model J1 = P [H2SO4]^n; where P is the prefactor containing chemical and physical information of the nucleation process, and n is the nucleation exponent. With the so called activation and kinetic nucleation mechanisms, n takes the values 1 and 2, respectively, and most field studies show n to fall between these two values. For the SPC data, the nucleation exponent was higher than 2 for both individual days and for all nucleation days as a whole. In the light of the obtained results we will discuss the nucleation mechanism, composition of the nucleation mode particles, and the role of other gases (such as ammonia and water vapor) in the formation of new particles in SPC in more detail.

Hamed, Amar; Plaß-Dülmer, Christian; Elste, Thomas; Stange, Georg; Decesari, Stefano; Carbone, Claudio; Facchini, Maria Cristina; Joutsensaari, Jorma; Laaksonen, Ari

2010-05-01

127

Gas-phase chemistry of molecular containers.  

PubMed

The remarkable technical advances in mass spectrometry during the last decades, including soft ionisation techniques, the coupling of electrospray ionisation to flow reactors, and the broad scope of tandem mass spectrometric experiments applicable to mass-selected ions allow investigating the chemistry of molecular capsules in solution as well as in the absence of any environment. With these methods, mass spectrometry is capable of answering many questions starting from providing analytical characterisation data (elemental composition, stoichiometry, etc.) to structural aspects (connectivities, positions of building blocks in supramolecular complexes) and to the examination of solution and gas-phase reactivity including reactions inside molecular containers. The present article reviews this work with a focus rather on the chemical questions that can be answered than on the technical specialities of (tandem) mass spectrometry. PMID:24956973

Qi, Zhenhui; Heinrich, Thomas; Moorthy, Suresh; Schalley, Christoph A

2015-01-21

128

Transferring pharmaceuticals into the gas phase  

NASA Astrophysics Data System (ADS)

The dissolution of molecules of biological interest in supercritical carbon dioxide is investigated using pulsed molecular beam mass spectrometry. Due to the mild processing temperatures of most supercritical fluids, their adiabatic expansion into vacuum permits to transfer even thermally very sensitive substances into the gas phase, which is particularly attractive for pharmaceutical and biomedical applications. In addition, supercritical CO2constitutes a chemically inert solvent that is compatible with hydrocarbon-free ultrahigh vacuum conditions. Here, we report on the dissolution and pulsed supersonic jet expansion of caffeine (C8H10N4O2), the provitamin menadione (C11H8O2), and the amino acid derivative l-phenylalanine tert-butyl ester hydrochloride (C6H5CH2CH(NH2)COOC(CH3)3[dot operator]HCl), into vacuum. An on-axis residual gas analyzer is used to monitor the relative amounts of solute and solvent in the molecular beam as a function of solvent densityE The excellent selectivity and sensitivity provided by mass spectrometry permits to probe even trace amounts of solutes. The strong density variation of CO2 close to the critical point results in a pronounced pressure dependence of the relative ion currents of solute and solvent molecules, reflecting a substantial change in solubility.

Christen, Wolfgang; Krause, Tim; Rademann, Klaus

2008-11-01

129

Gas: A Neglected Phase in Remediation of Metals and Radionuclides  

SciTech Connect

The gas phase is generally ignored in remediation of metals and radionuclides because it is assumed that there is no efficient way to exploit it. In the literal sense, all remediations involve the gas phase because this phase is linked to the liquid and solid phases by vapor pressure and thermodynamic relationships. Remediation methods that specifically use the gas phase as a central feature have primarily targeted volatile organic contaminants, not metals and radionuclides. Unlike many organic contaminants, the vapor pressure and Henry's Law constants of metals and radionuclides are not generally conducive to direct air stripping of dissolved contaminants. Nevertheless, the gas phase can play an important role in remediation of inorganic contaminants and provide opportunities for efficient, cost effective remediation. The objective here is to explore ways in which manipulation of the gas phase can be used to facilitate remediation of metals and radionuclides.

Denham, Miles E.; Looney, Brian B

2005-09-28

130

The VRT gas turbine combustor - Phase II  

NASA Technical Reports Server (NTRS)

An innovative annular combustor configuration is being developed for aircraft and other gas turbine engines. This design has the potential of permitting higher turbine inlet temperatures by reducing the pattern factor and providing a major reduction in NO(x) emission. The design concept is based on a Variable Residence Time (VRT) technique which allows large fuel particles adequate time to completely burn in the circumferentially mixed primary zone. High durability of the combustor is achieved by dual-function use of the incoming air. In Phase I, the feasibility of the concept was demonstrated by water analogue tests and 3D computer modeling. The flow pattern within the combustor was as predicted. The VRT combustor uses only half the number of fuel nozzles of the conventional configuration. In Phase II, hardware was designed, procured, and tested under conditions simulating typical supersonic civil aircraft cruise conditions to the limits of the rig. The test results confirmed many of the superior performance predictions of the VRT concept. The Hastelloy X liner showed no signs of distress after nearly six hours of tests using JP5 fuel.

Melconian, Jerry O.; Mongia, Hukam C.; Nguyen, Hung L.

1992-01-01

131

Nucleation at the Contact Line Observed on Nanotextured Surfaces  

NASA Astrophysics Data System (ADS)

It has been conjectured that roughness plays a role in surface nucleation, the tendency for freezing to begin preferentially at the liquid-gas interface. Using high speed imaging, we sought evidence for freezing at the contact line on catalyst substrates with imposed characteristic length scales (texture). Length scales consistent with the critical nucleus size and with ? ˜? /? , where ? is a relevant line tension and ? is the surface tension, range from nanometers to micrometers. It is found that nanoscale texture causes a shift in the nucleation of ice in supercooled water to the three-phase contact line, while microscale texture does not.

Gurganus, C. W.; Charnawskas, J. C.; Kostinski, A. B.; Shaw, R. A.

2014-12-01

132

Nucleation at the contact line observed on nanotextured surfaces.  

PubMed

It has been conjectured that roughness plays a role in surface nucleation, the tendency for freezing to begin preferentially at the liquid-gas interface. Using high speed imaging, we sought evidence for freezing at the contact line on catalyst substrates with imposed characteristic length scales (texture). Length scales consistent with the critical nucleus size and with ???/?, where ? is a relevant line tension and ? is the surface tension, range from nanometers to micrometers. It is found that nanoscale texture causes a shift in the nucleation of ice in supercooled water to the three-phase contact line, while microscale texture does not. PMID:25526136

Gurganus, C W; Charnawskas, J C; Kostinski, A B; Shaw, R A

2014-12-01

133

Nucleation in the presence of long-range interactions. [performed on ferroelectric barium titanate  

NASA Technical Reports Server (NTRS)

Unlike droplet nucleation near a liquid-gas critical point, the decay of metastable phases in crystalline materials is strongly affected by the presence of long-range forces. Field quench experiments performed on the ferroelectric barium titanate indicate that nucleation in this material is markedly different from that observed in liquids. In this paper, a theory for nucleation at a first-order phase transition in which the mediating forces are long range is presented. It is found that the long-range force induces cooperative nucleation and growth processes, and that this feedback mechanism produces a well-defined delay time with a sharp onset in the transformation to the stable phase. Closed-form expressions for the characteristic onset time and width of the transition are developed, in good agreement with numerical and experimental results.

Chandra, P.

1989-01-01

134

Gas-phase ionisation of sputtered rare gas atoms  

Microsoft Academic Search

During bombardment of solid samples with rare gas ions, charge-transfer events can convert reemitted rare gas atoms to positively charged ions. In analytical applications of secondary ion mass spectrometry (SIMS) this mechanism of ion formation is of considerable interest because, owing to their high ionisation potential, the ion fraction of sputtered rare gas atoms is very low. A quadrupole-based SIMS

K. Wittmaack

2008-01-01

135

Single Particle Laser Mass Spectrometry Applied to Differential Ice Nucleation Experiments at the AIDA Chamber  

SciTech Connect

Experiments conducted at the Aerosol Interactions and Dynamics in the Atmosphere (AIDA) chamber located in Karlsruhe, Germany permit investigation of particle properties that affect the nucleation of ice at temperature and water vapor conditions relevant to cloud microphysics and climate issues. Ice clouds were generated by heterogeneous nucleation of Arizona test dust (ATD), illite, and hematite and homogeneous nucleation of sulfuric acid. Ice crystals formed in the chamber were inertially separated from unactivated, or ‘interstitial’ aerosol particles with a pumped counterflow virtual impactor (PCVI), then evaporated. The ice residue (i.e., the aerosol which initiated ice nucleation plus any material which was scavenged from the gas- and/or particle-phase), was chemically characterized at the single particle level using a laser ionization mass spectrometer. In this manner the species that first nucleated ice could be identified out of a mixed aerosol population in the chamber. Bare mineral dust particles were more effective ice nuclei (IN) than similar particles with a coating. Metallic particles from contamination in the chamber initiated ice nucleation before other species but there were few enough that they did not compromise the experiments. Nitrate, sulfate, and organics were often detected on particles and ice residue, evidently from scavenging of trace gas-phase species in the chamber. Hematite was a more effective ice nucleus than illite. Ice residue was frequently larger than unactivated test aerosol due to the formation of aggregates due to scavenging, condensation of contaminant gases, and the predominance of larger aerosol in nucleation.

Gallavardin, S. J.; Froyd, Karl D.; Lohmann, U.; Moehler, Ottmar; Murphy, Daniel M.; Cziczo, Dan

2008-08-26

136

SHORT COMMUNICATION Gas-Phase Separations of Protease Digests  

E-print Network

SHORT COMMUNICATION Gas-Phase Separations of Protease Digests Stephen J. Valentine, Anne E University, Bloomington, Indiana, USA A mixture of peptides from a complete tryptic digest of ubiquitin has and identify peptides from a tryptic digest of ubiquitin. The mixture was electrosprayed into the gas phase

Clemmer, David E.

137

Pressure Dependence of Gas-Phase Reaction Rates  

ERIC Educational Resources Information Center

It is presented that only simple concepts, mainly taken from activated-complex or transition-state theory, are required to explain and analytically describe the influence of pressure on gas-phase reaction kinetics. The simplest kind of elementary gas-phase reaction is a unimolecular decomposition reaction.

De Persis, Stephanie; Dollet, Alain; Teyssandier, Francis

2004-01-01

138

Instabilities in Lean Gas-Phase Combustion  

NASA Astrophysics Data System (ADS)

Lean burning is the burning of fuel-air mixtures with less than the chemically- balanced (stoichiometric) mixture. It produces a significant increase in fuel efficiency and reduction in pollution. However, the limits and control of lean burning are still not well understood.This is the motivation behind the study of instabilities in lean gas-phase combustion under microgravity conditions via direct numerical simulations and comparison of the results with experimental data.The goal is to gain fundamental insights in order to identify and understand the intrinsic chemical and fluid dynamical mechanisms responsible for these instabilities.The potential of this microgravity combustion research includes the development of technology that would reduce pollution and fire and explosion hazards, improve hazardous waste incineration and increase efficiency of the conversion of chemical energy to electric power or motive force.The results from this fundamental research will thus benefit chemical engineering and power generation. Its wide range of applications in industry includes lean-burning car engines.

Schneider, K.; Bockhorn, H.; Eigenbrod, Ch.; Emerson, D.; Haldenwang, P.; Hoffmann, F.; Roekaerts, D.; Ronney, P.; Triebel, W.; Tummers, M.

2005-06-01

139

GAS-PHASE HOLDUP IN A SLURRY-BUBBLE COLUMN  

Microsoft Academic Search

Total and sectional gas-phase holdups are measured in a wide (0.305 m internal diameter) and long (3.7 m) glass bubble column al ambient conditions as a function of superficial gas velocity. Sectional gas holdup values vary along the length of the column and decrease as the height above the gas distributor plate increases in the transitional and turbulent flow regimes.

J. W. ZHU; V. H. TRIVEDI; S. C. SAXENA

1997-01-01

140

Gas-phase nitronium ion affinities.  

PubMed Central

Evaluation of nitronium ion-transfer equilibria, L1NO2+ + L2 = L2NO2+ + L1 (where L1 and L2 are ligands 1 and 2, respectively) by Fourier-transform ion cyclotron resonance mass spectrometry and application of the kinetic method, based on the metastable fragmentation of L1(NO2+)L2 nitronium ion-bound dimers led to a scale of relative gas-phase nitronium ion affinities. This scale, calibrated to a recent literature value for the NO2+ affinity of water, led for 18 ligands, including methanol, ammonia, representative ketones, nitriles, and nitroalkanes, to absolute NO2+ affinities, that fit a reasonably linear general correlation when plotted vs. the corresponding proton affinities (PAs). The slope of the plot depends to a certain extent on the specific nature of the ligands and, hence, the correlations between the NO2+ affinities, and the PAs of a given class of compounds display a better linearity than the general correlation and may afford a useful tool for predicting the NO2+ affinity of a molecule based on its PA. The NO2+ binding energies are considerably lower than the corresponding PAs and well below the binding energies of related polyatomic cations, such as NO+, a trend consistent with the available theoretical results on the structure and the stability of simple NO2+ complexes. The present study reports an example of extension of the kinetic method to dimers, such as L1(NO2+)L2, bound by polyatomic ions, which may considerably widen its scope. Finally, measurement of the NO2+ affinity of ammonia allowed evaluation of the otherwise inaccessible PA of the amino group of nitramide and, hence, direct experimental verification of previous theoretical estimates. PMID:11607578

Cacace, F; de Petris, G; Pepi, F; Angelelli, F

1995-01-01

141

Solid-liquid surface tensions of critical nuclei and nucleation barriers from a phase-field-crystal study of a model binary alloy using finite system sizes  

NASA Astrophysics Data System (ADS)

Phase-field-crystal (PFC) modeling has emerged as a computationally efficient tool to address crystal growth phenomena on atomistic length and diffusive time scales. We use a two-dimensional phase-field-crystal model for a binary system based on Elder et al. [Phys. Rev. B 75, 064107 (2007), 10.1103/PhysRevB.75.064107] to study critical nuclei and their liquid-solid phase boundaries, in particular the nucleus size dependence of the liquid-solid interface tension as well as of the nucleation barrier. Critical nuclei are stabilized in finite systems of various sizes, however, the extracted interface tension as function of the nucleus radius r is independent of system size. We suggest a phenomenological expression to describe the dependence of the extracted interface tension on the nucleus radius r for the liquid-solid system. Moreover, the numerical PFC results show that this dependency can not be fully described by the nonclassical Tolman formula.

Choudhary, Muhammad Ajmal; Kundin, Julia; Emmerich, Heike; Oettel, Martin

2014-08-01

142

Metadynamics studies of crystal nucleation  

PubMed Central

Crystallization processes are characterized by activated events and long timescales. These characteristics prevent standard molecular dynamics techniques from being efficiently used for the direct investigation of processes such as nucleation. This short review provides an overview on the use of metadynamics, a state-of-the-art enhanced sampling technique, for the simulation of phase transitions involving the production of a crystalline solid. In particular the principles of metadynamics are outlined, several order parameters are described that have been or could be used in conjunction with metadynamics to sample nucleation events and then an overview is given of recent metadynamics results in the field of crystal nucleation.

Giberti, Federico; Salvalaglio, Matteo; Parrinello, Michele

2015-01-01

143

Recent progress in understanding particle nucleation and growth  

PubMed Central

In the past half decade, several new tools have become available for investigating particle nucleation and growth. A number of joint field and laboratory studies exploiting some of these new measurement capabilities will be described and new insights shared. the ability to measure OH, SO2, H2SO4 and aerosol number and size distributions has made possible a comparison between H2SO4 production and loss onto particles in continental air masses. In regions remote from urban emissions, agreement is typically quite good. In contrast, joint field measurements of nucleation precursors such as gas phase H2SO4 and ultrafine particles suggest that classical bimolecular nucleation theory may not properly describe the tropospheric nucleation process. An alternative mechanism, possibly involving ammonia as a stabilizing agent for H2SO4/H2O molecular clusters is discussed. Finally, ultrafine particle measurements are shown to offer new opportunities for studying particle growth rates. Preliminary results suggest that in a remote continental air mass, gas phase H2SO4 uptake is far too slow to explain observed growth rates.

Eisele, F. L.; McMurry, P. H.

1997-01-01

144

Gas-Liquid Flows and Phase Separation  

NASA Technical Reports Server (NTRS)

Common issues for space system designers include:Ability to Verify Performance in Normal Gravity prior to Deployment; System Stability; Phase Accumulation & Shedding; Phase Separation; Flow Distribution through Tees & Manifolds Boiling Crisis; Heat Transfer Coefficient; and Pressure Drop.The report concludes:Guidance similar to "A design that operates in a single phase is less complex than a design that has two-phase flow" is not always true considering the amount of effort spent on pressurizing, subcooling and phase separators to ensure single phase operation. While there is still much to learn about two-phase flow in reduced gravity, we have a good start. Focus now needs to be directed more towards system level problems .

McQuillen, John

2004-01-01

145

Mixed Stationary Liquid Phases for Gas-Liquid Chromatography.  

ERIC Educational Resources Information Center

Describes a laboratory technique for use in an undergraduate instrumental analysis course that, using the interpretation of window diagrams, prepares a mixed liquid phase column for gas-liquid chromatography. A detailed procedure is provided. (BT)

Koury, Albert M.; Parcher, Jon F.

1979-01-01

146

Equilibrium structures from gas-phase electron-diffraction data   

E-print Network

For the past 75 years gas-phase electron diffraction (GED) has remained the most valuable technique for determining structures of small molecules, free from intermolecular interactions. Throughout this period many ...

McCaffrey, Philip D

2007-01-01

147

Multimaterial nanostructures Mimicking Electrodeposition in the Gas Phase  

E-print Network

in the Gas Phase [Ã?] Prof. H. O. Jacobs, J. J. Cole,[+] E.-C. Lin,[+] Dr. C. R. Barry Electrical Engineering for Selected-Area Fabrication of Multimaterial Nanostructures Jesse J. Cole, En-Chiang Lin, Chad R. Barry, and Heiko O. Jacobs* An in situ gas-phase process that produces charged streams of Au, Si, TiO2, ZnO, and Ge

Jacobs, Heiko O.

148

The gas phase oxidation of elemental mercury by ozone  

Microsoft Academic Search

The gas phase reaction between elemental mercury (Hg0) and ozone (03) has been studied in sunlight, in darkness, at different temperatures, and different surface-to-volume (s\\/v) ratios. At 03 concentrations above 20 ppm, a loss of Hg0 and a simultaneous formation of oxidized mercury (Hg(II)) was observed. The results suggest a partly heterogeneous reaction, with a gas phase rate constant of

B. Hall

1995-01-01

149

Gas phase reaction of sulfur trioxide with water vapor  

Microsoft Academic Search

Sulfur trioxide (SO3) has long been known to react with water to produce sulfuric acid (H2S04). It has been commonly assumed that the gas phase reaction in the Earth`s atmosphere between SO3 and water vapor to produce sulfuric acid vapor is an important step in the production of sulfuric acid aerosol particles. The kinetics of the gas phase reaction of

C. E. Kolb; M. J. Molina; J. T. Jayne; R. F. Meads; D. R. Worsnop; A. A. Viggiano

1994-01-01

150

Fission and Nuclear Liquid-Gas Phase Transition  

E-print Network

The temperature dependence of the liquid-drop fission barrier is considered, the critical temperature for the liquid-gas phase transition in nuclear matter being a parameter. Experimental and calculated data on the fission probability are compared for highly excited $^{188}$Os. The calculations have been made in the framework of the statistical model. It is concluded that the critical temperature for the nuclear liquid--gas phase transition is higher than 16 MeV.

E. A. Cherepanov; V. A. Karnaukhov

2007-03-30

151

Optimal grade transitions in a gas phase polyethylene reactor  

Microsoft Academic Search

This paper reports that using gas-phase technology many grades of polyethylene can be produced in a single reactor. For a series of three polyethylene products, model-based dynamic optimization is used to determine optimal grade changeover policies. Optimal manipulated variable profiles are determined for hydrogen and butene feed rates, reactor temperature setpoint, gas bleed flow, catalyst feed rate, and bed level

K. B. McAuley; J. F. MacGregor

1992-01-01

152

DSMC Convergence for Microscale Gas-Phase Heat Conduction  

Microsoft Academic Search

The convergence of Bird's Direct Simulation Monte Carlo (DSMC) method is investigated for gas-phase heat conduction at typical microscale conditions. A hard-sphere gas is confined between two fully accommodating walls of unequal temperature. Simulations are performed for small system and local Knudsen numbers, so continuum flow exists outside the Knudsen layers. The ratio of the DSMC thermal conductivity to the

D. J. Rader; M. A. Gallis; J. R. Torczynski

2004-01-01

153

High-speed rewritable DVD up to 20 m/s with nucleation-free eutectic phase-change material of Ge(Sb70Te30)+Sb  

NASA Astrophysics Data System (ADS)

High speed overwriting capability of the nucleation-free and growth-dominant eutectic Ge(Sb70Te30)+Sb phase- change material, and its application to high speed overwritable DVD and CD, are discussed. The addition of Ge to Sb70Te30+Sb binary system could effectively suppress the nucleation in recrystallization process, while high Sb/Te ratio could realize a selective enhancement of crystalline growth-speed initiated from the boundary of an amorphous mark and its crystalline background. This resolved a trade-off in high speed erasure and archival stability of amorphous marks. Highly enhanced crystalline growth also caused serious recrystallization during amorphous mark formation, resulting in shrinkage of amorphous mark size (premature cooling issue). This premature cooling issue as well as premature heating issue, in multiple pulse strategy with such a short writing and cooling pulse as below 10 nsec at high clock frequency of > 100 MHz for over 4X speed rewritable DVD, were resolved with a 2T-period based multiple pulse strategy. Thus, feasibility of 2 - 4.8X CAV operatable rewritable DVD and 16X CD-RW was demonstrated.

Horie, Michikazu; Nobukuni, Natsuko; Kiyono, Kenjirou; Ohno, Takashi

2000-09-01

154

Simulation Approach for Microscale Noncontinuum Gas-Phase Heat Transfer  

NASA Astrophysics Data System (ADS)

In microscale thermal actuators, gas-phase heat transfer from the heated beams to the adjacent unheated substrate is often the main energy-loss mechanism. Since the beam-substrate gap is comparable to the molecular mean free path, noncontinuum gas effects are important. A simulation approach is presented in which gas-phase heat transfer is described by Fourier's law in the bulk gas and by a wall boundary condition that equates the normal heat flux to the product of the gas-solid temperature difference and a heat transfer coefficient. The dimensionless parameters in this heat transfer coefficient are determined by comparison to Direct Simulation Monte Carlo (DSMC) results for heat transfer from beams of rectangular cross section to the substrate at free-molecular to near-continuum gas pressures. This simulation approach produces reasonably accurate gas-phase heat-transfer results for wide ranges of beam geometries and gas pressures. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Torczynski, J. R.; Gallis, M. A.

2008-11-01

155

Constant volume gas cell optical phase-shifter  

DOEpatents

A constant volume gas cell optical phase-shifter, particularly applicable for phase-shifting interferometry, contains a sealed volume of atmospheric gas at a pressure somewhat different than atmospheric. An optical window is present at each end of the cell, and as the length of the cell is changed, the optical path length of a laser beam traversing the cell changes. The cell comprises movable coaxial tubes with seals and a volume equalizing opening. Because the cell is constant volume, the pressure, temperature, and density of the contained gas do not change as the cell changes length. This produces an exactly linear relationship between the change in the length of the gas cell and the change in optical phase of the laser beam traversing it. Because the refractive index difference between the gas inside and the atmosphere outside is very much the same, a large motion must be made to change the optical phase by the small fraction of a wavelength that is required by phase-shifting interferometry for its phase step. This motion can be made to great fractional accuracy.

Phillion, Donald W. (Dublin, CA)

2002-01-01

156

Superfluid phases of the three-species fermion gas  

SciTech Connect

We discuss the zero temperature phase diagram of a dilute gas with three fermionic species. We make use of solvable limits to conjecture the behavior of the system in the 'unitary' regions. The physics of the Thomas-Efimov effect plays a role in these considerations. We find a rich phase diagram with superfluid, gapless superfluid and inhomogeneous phases with different symmetry breaking patterns. We then discuss one particular possible experimental implementation in a system of {sup 6}Li atoms and the possible phases arising in this system as an external magnetic field is varied across three overlapping Feshbach resonances. We also suggest how to experimentally distinguish the different phases.

Bedaque, Paulo F. [Lawrence-Berkeley Laboratory, Berkeley, CA 94720 (United States); University of Maryland, College Park, MD 20742 (United States)], E-mail: bedaque@umd.edu; D'Incao, Jose P. [Department of Physics, Kansas State University, Manhattan, KS 66506 (United States)], E-mail: jpdincao@jila.colorado.edu

2009-08-15

157

A gas-phase solvent effect  

NASA Astrophysics Data System (ADS)

Quantum chemical calculations at the CP-dG2thaw and MP2(thaw)/B4G levels of theory are reported for the bare HOMg+OCO ion resulting from addition of CO2 to HOMg+, and to its mono-, di- and tri-hydrated forms. These calculations are used to determine bond dissociation energy (BDE) values for the (H2O)n(CO2)iHOMg+-OH2 (n = 0-2; i = 0, 1) and (H2O)nHOMg+-OCO (n = 0-3) bonds, as well as to ascertain the relative energies for several key stationary points on each of the HOMg+·(H2O)n·CO2 (n = 0-3) potential energy surfaces. Three principal findings emerge from these calculations. First, in contrast to the isoelectronic system NaOH + CO2 --> NaO2COH held to play a leading role in noctilucent cloud nucleation, the reaction of HOMg+ + CO2 does not result in formation of the magnesium bicarbonate cation Mg+O2COH. Second, the cumulative Mg+-ligand bond energies for complexes of HOMg+ with several H2O and CO2 molecules rapidly approach, and then exceed, the available Mg+ recombination energy, indicating that dissociative recombination of HOMg+·(H2O)n·CO2 (or its bicarbonate-containing isomer Mg+O2COH·(H2O)n) is likely to result in the production of molecular Mg-containing neutrals. Third, we find that hydration exhibits a remarkable influence on the reactivity of HOMg+ with mesospheric CO2: addition of CO2 to bare HOMg+ does not result in bicarbonate formation, nor do the reactions of HOMg+·CO2 and HOMg+·OH2·CO2 with H2O, but the reaction of HOMg+·(OH2)2·CO2 with H2O leads to two possible bicarbonate-containing products (H2O)2·Mg+O2COH and (H2O)3·Mg+O2COH. The former product channel, which involves association followed by H2O loss, is judged to be an unusual example of a catalytic process in which the principal contribution of the H2O [`]catalyst' is steric.

Petrie, Simon

2006-08-01

158

Effect of nucleated Cu phase on magnetic properties and electronic structures in bcc Fe: Ab initio study  

NASA Astrophysics Data System (ADS)

Using the first-principles calculations, the change in magnetism and electronic structures during Cu nucleation in bcc Fe system was investigated. For modeling the Fe-rich bcc FeCu alloy, FexCu1-x (x ?0.75) were employed in the supercell system. Nonmagnetic Cu atoms were precipitated on the (100) plane of bcc Fe crystal, whereas the magnetized Cu atoms preferred to be precipitated on the (110) plane. Magnetization energies showed a linear decrease as the Cu concentration increased in bcc Fe. The magnetic moments of Fe atoms increased for larger concentration of Cu atoms. Electron density of states showed that the enhanced magnetic moment of Fe atoms resulted from the shift of minority spin states toward higher levels, which was associated with the bond formation between Cu and Fe atoms.

Choi, Heechae; Kim, Chiho; Chung, Yong-Chae

2009-10-01

159

Microfabricated Gas Phase Chemical Analysis Systems  

SciTech Connect

A portable, autonomous, hand-held chemical laboratory ({micro}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.

FRYE-MASON,GREGORY CHARLES; HELLER,EDWIN J.; HIETALA,VINCENT M.; KOTTENSTETTE,RICHARD; LEWIS,PATRICK R.; MANGINELL,RONALD P.; MATZKE,CAROLYN M.; WONG,CHUNGNIN C.

1999-09-16

160

Microfabricated Gas Phase Chemical Analysis Systems  

SciTech Connect

A portable, autonomous, hand-held chemical laboratory ({mu}ChemLab{trademark}) is being developed for trace detection (ppb) of chemical warfare (CW) agents and explosives in real-world environments containing high concentrations of interfering compounds. Microfabrication is utilized to provide miniature, low-power components that are characterized by rapid, sensitive and selective response. Sensitivity and selectivity are enhanced using two parallel analysis channels, each containing the sequential connection of a front-end sample collector/concentrator, a gas chromatographic (GC) separator, and a surface acoustic wave (SAW) detector. Component design and fabrication and system performance are described.

Casalnuovo, Stephen A.; Frye-Mason, Gregory C; Heller, Edwin J.; Hietala, Vincent M.; Kottenstette, Richard J.; Lewis, Patrick R.; Manginell, Ronald P.; Matzke, Carolyn M.; Wong, C. Channy

1999-08-02

161

Specific and reproducible gas sensors utilizing gas-phase chemical reaction on organic transistors.  

PubMed

Utilizing a textbook reaction on the surface of an organic active channel, achieves sensitive detection of HCl, NH3 and NO2, with good selectivity, excellent reproducibility, and satisfactory stability. These results reveal gas-phase reaction assisted detection as a unique and promising approach to construct practical applicable gas sensors with typical organic transistors. PMID:24510689

Zang, Yaping; Zhang, Fengjiao; Huang, Dazhen; Di, Chong-an; Meng, Qing; Gao, Xike; Zhu, Daoben

2014-05-01

162

Capillary gas chromatography with two new moderately high temperature phases.  

NASA Technical Reports Server (NTRS)

Gas chromatography test results are presented for two new moderately high-temperature phases of Dexsil 400-GC with free hydroxyl end groups (uncapped) and with end groups covered by trimethyl silyl groups (capped). The two Dexsil 400-GC phases were tested for their ability to resolve N-TFA-DL-(+)-2-butyl esters and n-butyl esters, as well as fatty acid methyl esters and hydrocarbon standards. Generally the more polar uncapped phase was superior to the capped phase in all separation comparisons, except for the hydrocarbons.

Pollock, G. E.

1972-01-01

163

Freeze drying for gas chromatography stationary phase deposition  

DOEpatents

The present disclosure relates to methods for deposition of gas chromatography (GC) stationary phases into chromatography columns, for example gas chromatography columns. A chromatographic medium is dissolved or suspended in a solvent to form a composition. The composition may be inserted into a chromatographic column. Alternatively, portions of the chromatographic column may be exposed or filled with the composition. The composition is permitted to solidify, and at least a portion of the solvent is removed by vacuum sublimation.

Sylwester, Alan P. (Livermore, CA)

2007-01-02

164

Effect of phase behavior on bypassing in enriched gas floods  

SciTech Connect

Enriched gas floods incorporate a complex interaction of heterogeneity, fingering, multiphase flow, and phase behavior. Experiments and simulations indicate that the optimum solvent enrichment in high-viscosity-ratio secondary gas floods can be below minimum miscibility enrichment (MME). The compositional path and resulting mobility profile in multidimensional multiple-contact miscible (MCM) or immiscible floods are different from their 1D counterparts for high-viscosity-ratio floods in heterogeneous media.

Burger, J.E.; Bhogeswara, R.; Mohanty, K.K. (Univ. of Houston, TX (United States))

1994-05-01

165

Collision-induced gas phase dissociation rates  

NASA Technical Reports Server (NTRS)

The Landau-Zener theory of reactive cross sections was applied to diatomic molecules dissociating from a ladder of vibrational states. The result predicts a dissociation rate that is quite well duplicated by an Arrhenius function having a preexponential temperature dependence of about T(sub -1/2), at least for inert collision partners. This relation fits experimental data reasonably well. The theory is then used to calculate the effect of vibrational nonequilibrium on dissociation rate. For Morse oscillators, the results are about the same as given by Hammerling, Kivel, and Teare in their analytic approximation for harmonic oscillators, though at very high temperature a correction for the partition function limit is included. The empirical correction for vibration nonequilibrium proposed by Park, which is a convenient algorithm for CFD calculations, is modified to prevent a drastic underestimation of dissociation rates that occurs with this method when vibrational temperature is much smaller than the kinetic temperature of the gas.

Hansen, C. Frederick

1990-01-01

166

CHEMKIN2. General Gas-Phase Chemical Kinetics  

SciTech Connect

CHEMKIN is a high-level tool for chemists to use to describe arbitrary gas-phase chemical reaction mechanisms and systems of governing equations. It remains, however, for the user to select and implement a solution method; this is not provided. It consists of two major components: the Interpreter and the Gas-phase Subroutine Library. The Interpreter reads a symbolic description of an arbitrary, user-specified chemical reaction mechanism. A data file is generated which forms a link to the Gas-phase Subroutine Library, a collection of about 200 modular subroutines which may be called to return thermodynamic properties, chemical production rates, derivatives of thermodynamic properties, derivatives of chemical production rates, or sensitivity parameters. Both single and double precision versions of CHEMKIN are included. Also provided is a set of FORTRAN subroutines for evaluating gas-phase transport properties such as thermal conductivities, viscosities, and diffusion coefficients. These properties are an important part of any computational simulation of a chemically reacting flow. The transport properties subroutines are designed to be used in conjunction with the CHEMKIN Subroutine Library. The transport properties depend on the state of the gas and on certain molecular parameters. The parameters considered are the Lennard-Jones potential well depth and collision diameter, the dipole moment, the polarizability, and the rotational relaxation collision number.

Rupley, F.M. [Sandia National Labs., Livermore, CA (United States)

1992-01-24

167

Gas purification in the dense phase at the CATS terminal  

SciTech Connect

The purification and transportation of natural gas at very high pressures can help to minimize the capital cost of pipelines and processing equipment. However, complex mixtures of hydrocarbons undergo unusual phase changes, such as retrograde condensation, as the temperature and pressure are altered. The Central Area Transmission System (CATS) is a joint venture of Amoci, BG, Amerada Hess, Phillips, Agip and Fina operated by Amoco on behalf of the owners. The design of the CATS terminal has provided an interesting processing challenge. The terminal receives a total of 1.6 Bscf/d of rich gas from a number of offshore fields. All are relatively sweet but the small amounts of H{sub 2}S and Hg are removed. Fixed bed technology was selected as the most economic purification process, while minimizing hydrocarbon loss and operator involvement. Conventionally, the raw gas would be split into the different hydrocarbon fractions and each would be processed separately. This would require the installation of a large number of reactors. A more elegant solution is to treat the gas on arrival at the terminal in the dense phase. This option raised questions around whether a fixed bed would be prone to fouling, could the pressure drop be kept low enough to avoid phase separation and would inadvertent wetting by condensation cause problems. Details are given of the test work carried out to prove the viability of using fixed bed technology for dense phase gas processing, the eventual design adopted and the performance over the first year of service.

Openshaw, P.J.; Carnell, P.J.H.; Rhodes, E.F.

1999-07-01

168

Improvement and further development in CESM/CAM5: gas-phase chemistry and inorganic aerosol treatments  

NASA Astrophysics Data System (ADS)

Gas-phase chemistry and subsequent gas-to-particle conversion processes such as new particle formation, condensation, and thermodynamic partitioning have large impacts on air quality, climate, and public health through influencing the amounts and distributions of gaseous precursors and secondary aerosols. Their roles in global air quality and climate are examined in this work using the Community Earth System Model version 1.0.5 (CESM1.0.5) with the Community Atmosphere Model version 5.1 (CAM5.1) (referred to as CESM1.0.5/CAM5.1). CAM5.1 includes a simple chemistry that is coupled with a 7-mode prognostic Modal Aerosol Model (MAM7). MAM7 includes classical homogenous nucleation (binary and ternary) and activation nucleation (empirical first-order power law) parameterizations, and a highly simplified inorganic aerosol thermodynamics treatment that only simulates particulate-phase sulfate and ammonium. In this work, a new gas-phase chemistry mechanism based on the 2005 Carbon Bond Mechanism for Global Extension (CB05_GE) and several advanced inorganic aerosol treatments for condensation of volatile species, ion-mediated nucleation (IMN), and explicit inorganic aerosol thermodynamics for sulfate, ammonium, nitrate, sodium, and chloride have been incorporated into CESM/CAM5.1-MAM7. Compared to the simple gas-phase chemistry, CB05_GE can predict many more gaseous species, and thus could improve model performance for PM2.5, PM10, PM components, and some PM gaseous precursors such as SO2 and NH3 in several regions as well as aerosol optical depth (AOD) and cloud properties (e.g., cloud fraction (CF), cloud droplet number concentration (CDNC), and shortwave cloud forcing, SWCF) on the global scale. The modified condensation and aqueous-phase chemistry could further improve the prediction of additional variables such as HNO3, NO2, and O3 in some regions, and new particle formation rate (J) and AOD on the global scale. IMN can improve the prediction of secondary PM2.5 components, PM2.5, and PM10 over Europe as well as AOD and CDNC on the global scale. The explicit inorganic aerosol thermodynamics using the ISORROPIA II model improves the prediction of all major PM2.5 components and their gaseous precursors in some regions as well as downwelling shortwave radiation, SWCF, and cloud condensation nuclei at a supersaturation of 0.5% on the global scale. For simulations of 2001-2005 with all the modified and new treatments, the improved model predicts that on global average, SWCF increases by 2.7 W m-2, reducing the normalized mean bias (NMB) of SWCF from -5.4 to 1.2%. Uncertainties in emissions can largely explain the inaccurate prediction of precursor gases (e.g., SO2, NH3, and NO) and primary aerosols (e.g., black carbon and primary organic matter). Additional factors leading to the discrepancies between model predictions and observations include assumptions associated with equilibrium partitioning for fine particles assumed in ISORROPIA II, irreversible gas/particle mass transfer treatment for coarse particles, uncertainties in model treatments such as dust emissions, secondary organic aerosol formation, multi-phase chemistry, cloud microphysics, aerosol-cloud interaction, dry and wet deposition, and model parameters (e.g., accommodation coefficients and prefactors of the nucleation power law) as well as uncertainties in model configuration such as the use of a coarse-grid resolution.

He, J.; Zhang, Y.

2014-09-01

169

Gas-phase azide functionalization of carbon.  

PubMed

Tailoring the surface and interfacial properties of inexpensive and abundant carbon materials plays an increasingly important role for innovative applications including those in electrocatalysis, energy storage, gas separations, and composite materials. Described here is the novel preparation and subsequent use of gaseous iodine azide for the azide modification of carbon surfaces. In-line generation of gaseous iodine azide from iodine monochloride vapor and solid sodium azide is safe and convenient. Immediate treatment of carbon surfaces with this gaseous stream of iodine azide provides a highly reproducible, selective, and scalable azide functionalization that minimizes waste and reduces deleterious side reactions. Among the possible uses of azide-modified surfaces, they serve as versatile substrates for the attachment of additional functionality by coupling with terminal alkynes under the mild copper-catalyzed azide-alkyne cycloaddition (CuAAC) "click" reaction. For instance, coupling ethynylferrocene to azide-modified glassy carbon surfaces achieves ferrocene coverage up to 8 × 10(13) molecules/cm(2) by voltammetric and XPS analyses. The 1,2,3-triazole linker formed during the CuAAC reaction is robust and hydrolytically stable in both aqueous 1 M HClO(4) and 1 M NaOH for at least 12 h at 100 °C. PMID:23301920

Stenehjem, Eric D; Ziatdinov, Vadim R; Stack, T Daniel P; Chidsey, Christopher E D

2013-01-23

170

Energy partitioning in elementary gas phase reactions  

NASA Astrophysics Data System (ADS)

During the last 2(1/2) years we: Measured the LIF excitation spectrum of H atoms dissociated by 193 nm light from cyclopentadiene and indene as well as the rate of dissociation of indene. A general relation is that the translational temperature of the H atoms and the vibrational temperature of the molecules before dissociation are equal. We measured the H atom channel in the photodissociation of ethylene at 193 nm. The LIF excitation spectrum was measured as well as the quantum yield. Isotope effects were observed and explained by RRKM theory in CH2CD2 and trans-CHDCHD. We studied the photodissociation of hydrogen molecules with two photon excited states of the rare gas atoms, 5p(01/2) of Kr and 6p(01/2) of Xe. A new much stronger source of Lyman alpha light at 121.6 nm enabled the study of processes in which a hydride is photodissociated at 121.6 nm and within the same pulse a second photon excites H atom fluorescence. For the first time the dynamics of photodissociation of methane, water, acetylene and HCl were measured at 121.6 nm. Large isotope effects were seen. In CH3D, CH2D and CD3H the H atoms were twice as likely to dissociate as the D atoms.

Bersohn, R.

171

Fluid dynamic numerical simulation of a gas phase polymerization reactor  

Microsoft Academic Search

SUMMARY This article presents preliminaryuid dynamic simulation results of ethylene polymerization dense ?uidized bed using the two-phaseow numerical code ESTET-ASTRID developed by Electricited e France for CFB boilers and based on the two-?uid modelling approach. The continuous phase consists of gas and the dispersed phase consists of catalyst particles. The particleuctuating motion is modelled using two-separate transport equations, on the

Anne Gobin; Hervé Neau; Olivier Simonin; Jean-Richard Llinas; Vince Reiling; Jean-Lofc Sélo

2003-01-01

172

Sustained Perchlorate Degradation in an Autotrophic, Gas-Phase,  

E-print Network

, The Pennsylvania State University, University Park, Pennsylvania16802 An autotrophic packed-bed biofilm reactorSustained Perchlorate Degradation in an Autotrophic, Gas-Phase, Packed-Bed Bioreactor J O E L P . M feed concentration of 50 mg/L to build up biofilm on the reactor packing. The reactor feed

173

Submission PDF Surfactants from the gas phase may enhance aerosol  

E-print Network

, methylglyoxal and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon up- take-phase methylglyoxal and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically to the adsorption of methylglyoxal and acetaldehyde to the gas- aerosol interface, leading to surface tension

Nenes, Athanasios

174

LOW COST IMAGER FOR POLLUTANT GAS LEAK DETECTION - PHASE II  

EPA Science Inventory

An inexpensive imaging Instrument to quickly locate leaks of methane and other greenhouse and VOC gases would reduce the cost and effort expended by industry to comply with EPA regulations. In Phase I, of this WBIR program, a new gas leak visualization camera was demonstrated...

175

Ion-Molecule Reactions in Gas Phase Radiation Chemistry.  

ERIC Educational Resources Information Center

Discusses some aspects of the radiation chemistry of gases, focusing on the ion-molecule and charge neutralization reactions which set study of the gas phase apart. Uses three examples that illustrate radiolysis, describing the radiolysis of (1) oxygen, (2) carbon dioxide, and (3) acetylene. (CS)

Willis, Clive

1981-01-01

176

First measurements of gas phase sulphuric acid in the stratosphere  

Microsoft Academic Search

Measurements of the abundance of gas phase sulfuric acid in the stratosphere are reported. Compositions and abundances of stratospheric negative ions were observed at an altitude of 36.5 km, and the presence of species containing sulfuric acid molecules attached to HSO4(-) core ions was detected. A proposed reaction scheme suggests that the cores of these ions are formed by reactions

F. Arnold; R. Fabian

1980-01-01

177

Negatively-charged helices in the gas phase.  

PubMed

A polyalanine-based peptide which forms a stable, negatively-charged ?-helix in the gas phase is reported. Addition of an N-terminal acidic residue forms a stabilizing hydrogen bond network and an electrostatic interaction with the helical dipole. Formation of this secondary structure was demonstrated using ion mobility-mass spectrometry and molecular modelling techniques. PMID:24901462

Johnson, Andrew R; Dilger, Jonathan M; Glover, Matthew S; Clemmer, David E; Carlson, Erin E

2014-08-18

178

Selected Examples of Gas-Phase Ion Chemistry Studies  

PubMed Central

Gas-phase ion chemistry is an area in mass spectrometry that has received much research interest since the mid fifties of the last century. Although the focus of mass spectrometric research has shifted the last twenty years largely to life science studies, including proteomics, genomics and metabolomics, there are still several groups in the world active in gas-phase ion chemistry of both positive and negative ions, either unimolecularly and/or bimolecularly. In this tutorial lecture the formation and determination of tautomeric ion structures and intra-ionic catalyzed tautomerization in the gas phase will be discussed. In addition, an example of formation of different tautomeric structures in protic and aprotic solvents under electrospray ionization conditions will be given, as established by gas-phase infrared multiphoton dissociation spectroscopy. This will be followed by presenting an example of time-resolved MS/MS which enables to identify the structure of an ion, generated at a particular molecular ion lifetime. At the end of the lecture the power of ion mobility will be shown in elucidating the mechanism of epimerization of bis-Tröger bases having chiral nitrogen centers. PMID:24349921

Nibbering, Nico M. M.

2013-01-01

179

Gas-phase silicon micromachining with xenon difluoride  

Microsoft Academic Search

Xenon difluoride is a gas phase, room temperature, isotropic silicon etchant with extremely high selectivity to many materials commonly used in microelectromechancial systems, including photoresists, aluminum, and silicon dioxide. Using a simple vacuum system, the effects of etch aperture and loading were explored for etches between 10 and 200 micrometers . Etch rates as high as 40 micrometers \\/minute were

Floy I. Chang; Richard Yeh; Gisela Lin; Patrick B. Chu; Eric G. Hoffman; Ezekiel J. Kruglick; Kristofer S. Pister; Michael H. Hecht

1995-01-01

180

MODELING OF THE GAS-PHASE OXIDATION OF CYCLOHEXANE  

E-print Network

), the elementary steps included in the models of the oxidation of cyclic alkanes are close to those proposed to describe the oxidation of acyclic alkanes. Consequently, it has been possible to obtain the model proposedMODELING OF THE GAS-PHASE OXIDATION OF CYCLOHEXANE Frédéric BUDA, Barbara HEYBERGER, René FOURNET

Boyer, Edmond

181

Nucleation and growth of magnetite from solution  

NASA Astrophysics Data System (ADS)

The formation of crystalline materials from solution is usually described by the nucleation and growth theory, where atoms or molecules are assumed to assemble directly from solution. For numerous systems, the formation of the thermodynamically stable crystalline phase is additionally preceded by metastable intermediates . More complex pathways have recently been proposed, such as aggregational processes of nanoparticle precursors or pre-nucleation clusters, which seem to contradict the classical theory. Here we show by cryogenic transmission electron microscopy that the nucleation and growth of magnetite—a magnetic iron oxide with numerous bio- and nanotechnological applications—proceed through rapid agglomeration of nanometric primary particles and that in contrast to the nucleation of other minerals, no intermediate amorphous bulk precursor phase is involved. We also demonstrate that these observations can be described within the framework of classical nucleation theory.

Baumgartner, Jens; Dey, Archan; Bomans, Paul H. H.; Le Coadou, Cécile; Fratzl, Peter; Sommerdijk, Nico A. J. M.; Faivre, Damien

2013-04-01

182

Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation  

NASA Astrophysics Data System (ADS)

During the FROST-2 (FReezing Of duST) measurement campaign conducted at the Leipzig Aerosol Cloud Interaction Simulator (LACIS), we investigated changes in the ice nucleation properties of 300 nm Arizona Test Dust mineral particles following thermochemical processing by varying amounts and combinations of exposure to sulphuric acid vapour, ammonia gas, water vapour, and heat. The processed particles' heterogeneous ice nucleation properties were determined in both the water subsaturated and supersaturated humidity regimes at -30 °C and -25 °C using Colorado State University's continuous flow diffusion chamber. The amount of sulphuric acid coating material was estimated by an aerosol mass spectrometer and from CCN-derived hygroscopicity measurements. The condensation of sulphuric acid decreased the dust particles' ice nucleation ability in proportion to the amount of sulphuric acid added. Heating the coated particles in a thermodenuder at 250 °C - intended to evaporate the sulphuric acid coating - reduced their freezing ability even further. We attribute this behaviour to accelerated acid digestion of ice active surface sites by heat. Exposing sulphuric acid coated dust to ammonia gas produced particles with similarly poor freezing potential; however a portion of their ice nucleation ability could be restored after heating in the thermodenuder. In no case did any combination of thermochemical treatments increase the ice nucleation ability of the coated mineral dust particles compared to unprocessed dust. These first measurements of the effect of identical chemical processing of dust particles on their ice nucleation ability under both water subsaturated and mixed-phase supersaturated cloud conditions revealed that ice nucleation was more sensitive to all coating treatments in the water subsaturated regime. The results clearly indicate irreversible impairment of ice nucleation activity in both regimes after condensation of concentrated sulphuric acid. This implies that the sulphuric acid coating caused permanent chemical and/or physical modification of the ice active surface sites; the possible dissolution of the coating during droplet activation did not restore all immersion/condensation-freezing ability.

Sullivan, R. C.; Petters, M. D.; Demott, P. J.; Kreidenweis, S. M.; Wex, H.; Niedermeier, D.; Hartmann, S.; Clauss, T.; Stratmann, F.; Reitz, P.; Schneider, J.; Sierau, B.

2010-12-01

183

Irreversible loss of ice nucleation active sites in mineral dust particles caused by sulphuric acid condensation  

NASA Astrophysics Data System (ADS)

During the FROST-2 (FReezing Of duST) measurement campaign conducted at the Leipzig Aerosol Cloud Interaction Simulator (LACIS), we investigated changes in the ice nucleation properties of 300 nm Arizona test dust mineral particles following thermochemical processing by varying amounts and combinations of exposure to sulphuric acid vapour, ammonia gas, water vapour, and heat. The processed aerosol's heterogeneous ice nucleation properties were determined in both the water subsaturated and supersaturated humidity regimes at -30 °C and -25 °C using Colorado State University's continuous flow diffusion chamber. The amount of sulphuric acid coating material was estimated by an aerosol mass spectrometer and from CCN-derived hygroscopicity measurements. The condensation of sulphuric acid decreased the dust particles' ice nucleation ability in proportion to the amount of sulphuric acid added. Heating the coated particles in a thermodenuder at 250 °C - intended to evaporate the sulphuric acid coating - reduced their freezing ability even further. We attribute this behaviour to accelerated acid digestion of ice active surface sites by heat. Exposing sulphuric acid coated dust to ammonia gas produced particles with similarly poor freezing potential; however a portion of their ice nucleation ability could be restored after heating in the thermodenuder. In no case did any combination of thermochemical treatments increase the ice nucleation ability of the coated mineral dust particles compared to unprocessed dust. These first measurements of the effect of identical chemical processing of dust particles on their ice nucleation ability in both water subsaturated and mixed-phase supersaturated cloud conditions revealed that ice nucleation was more sensitive to all coating treatments in the water subsaturated regime. The results clearly indicate irreversible impairment of ice nucleation activity in both regimes after condensation of concentrated sulphuric acid. This implies that the sulphuric acid coating caused permanent chemical and/or physical modification of the ice active surface sites; the possible dissolution of the coating during droplet activation did not restore all immersion/condensation-freezing ability.

Sullivan, R. C.; Petters, M. D.; Demott, P. J.; Kreidenweis, S. M.; Wex, H.; Niedermeier, D.; Hartmann, S.; Clauss, T.; Stratmann, F.; Reitz, P.; Schneider, J.

2010-07-01

184

Flavin adenine dinucleotide structural motifs: from solution to gas phase.  

PubMed

Flavin adenine dinucleotide (FAD) is involved in important metabolic reactions where the biological function is intrinsically related to changes in conformation. In the present work, FAD conformational changes were studied in solution and in gas phase by measuring the fluorescence decay time and ion-neutral collision cross sections (CCS, in a trapped ion mobility spectrometer, TIMS) as a function of the solvent conditions (i.e., organic content) and gas-phase collisional partner (i.e., N2 doped with organic molecules). Changes in the fluorescence decay suggest that FAD can exist in four conformations in solution, where the abundance of the extended conformations increases with the organic content. TIMS-MS experiments showed that FAD can exist in the gas phase as deprotonated (M = C27H31N9O15P2) and protonated forms (M = C27H33N9O15P2) and that multiple conformations (up to 12) can be observed as a function of the starting solution for the [M + H](+) and [M + Na](+)molecular ions. In addition, changes in the relative abundances of the gas-phase structures were observed from a "stack" to a "close" conformation when organic molecules were introduced in the TIMS cell as collision partners. Candidate structures optimized at the DFT/B3LYP/6-31G(d,p) were proposed for each IMS band, and results showed that the most abundant IMS band corresponds to the most stable candidate structure. Solution and gas-phase experiments suggest that the driving force that stabilizes the different conformations is based on the interaction of the adenine and isoalloxazine rings that can be tailored by the "solvation" effect created with the organic molecules. PMID:25222439

Molano-Arevalo, Juan Camilo; Hernandez, Diana R; Gonzalez, Walter G; Miksovska, Jaroslava; Ridgeway, Mark E; Park, Melvin A; Fernandez-Lima, Francisco

2014-10-21

185

Nucleation of copper during supersonic expansion  

SciTech Connect

Nucleation of copper vapor during gas expansion in a supersonic nozzle is investigated. Time scales for nucleation delay and supersaturation doubling are considered in establishing the need for non-steady state nucleation theory. A population balance model is constructed for tracking the size spectrum of stable clusters formed from self nucleation and exposed to supersaturated gas. It is found that at average cooling rates exceeding 10{sup 7} K/s, copper vapor exists in a highly nonequilibrium concentration at the nozzle exit. Copper condensation is severely limited by the nucleation kinetics and the available residence time. It is influenced by the monomer concentration and the nozzle exit pressure and temperature. The size spectrum of stable clusters is dominated by small clusters containing fewer than fifteen molecules. Nucleation persists throughout the expansion process because of the inability of the vapor condensation processes to relieve supersaturation buildup due to rapid gas cooling. Nucleation rate is sensitive to the surface energy of the clusters corresponding to the critical size. Monte-Carlo simulations of admissible cluster configurations are recommended for determining statistically-averaged surface energies of clusters containing two-to-twenty molecules. 7 refs., 10 figs., 6 tabs.

Ahluwalia, R.K.; Im, K.H.

1989-12-01

186

Gas Phase Reactivity of Carboxylates with N-Hydroxysuccinimide Esters  

NASA Astrophysics Data System (ADS)

N-hydroxysuccinimide (NHS) esters have been used for gas-phase conjugation reactions with peptides at nucleophilic sites, such as primary amines (N-terminus, ?-amine of lysine) or guanidines, by forming amide bonds through a nucleophilic attack on the carbonyl carbon. The carboxylate has recently been found to also be a reactive nucleophile capable of initiating a similar nucleophilic attack to form a labile anhydride bond. The fragile bond is easily cleaved, resulting in an oxygen transfer from the carboxylate-containing species to the reagent, nominally observed as a water transfer. This reactivity is shown for both peptides and non-peptidic species. Reagents isotopically labeled with O18 were used to confirm reactivity. This constitutes an example of distinct differences in reactivity of carboxylates between the gas phase, where they are shown to be reactive, and the solution phase, where they are not regarded as reactive with NHS esters.

Peng, Zhou; McGee, William M.; Bu, Jiexun; Barefoot, Nathan Z.; McLuckey, Scott A.

2015-01-01

187

Star formation via the phase transition of an adiabatic gas  

NASA Technical Reports Server (NTRS)

An analytic model based on a second-order accurate global virial analysis is used to describe two stable equilibrium states for rotating gas clouds: a pressure-supported, diffuse state and a rotationally supported, compact state. Diffuse and compact equilibrium sequences are identified along which slow, secular evolution of a gas cloud can occur. A virial analysis provides analytic expressions for the limiting masses of gas clouds at points of dynamical instability. The minimum mass below which external triggers of any amplitude cannot effectively induce star formation is identified for adiabatic gas clouds. It is suggested that fluctuations in the ISM of some galaxies may actually cause star formation to proceed primarily via a phase transition, rather than via the classical Jeans instability.

Tohline, Joel E.; Christodoulou, Dimitris M.

1988-01-01

188

Field driven ferromagnetic phase nucleation and propagation from the domain boundaries in antiferromagnetically coupled perpendicular anisotropy films  

SciTech Connect

We investigate the reversal process in antiferromagnetically coupled [Co/Pt]{sub X-1}/{l_brace}Co/Ru/[Co/Pt]{sub X-1}{r_brace}{sub 16} multilayer films by combining magnetometry and Magnetic soft X-ray Transmission Microscopy (MXTM). After out-of-plane demagnetization, a stable one dimensional ferromagnetic (FM) stripe domain phase (tiger-tail phase) for a thick stack sample (X=7 is obtained), while metastable sharp antiferromagnetic (AF) domain walls are observed in the remanent state for a thinner stack sample (X=6). When applying an external magnetic field the sharp domain walls of the thinner stack sample transform at a certain threshold field into the FM stripe domain wall phase. We present magnetic energy calculations that reveal the underlying energetics driving the overall reversal mechanisms.

Hauet, Thomas; Gunther, Christian M.; Hovorka, Ondrej; Berger, Andreas; Im, Mi-Young; Fischer, Peter; Hellwig, Olav

2008-12-09

189

Analysis of nonlinear model of gas dynamics in a vertical reactor for gas phase epitaxy  

NASA Astrophysics Data System (ADS)

In this paper, we consider a vertical reactor for gas phase epitaxy. Based on the recently obtained results of Pankratov and Bulaeva [2013, Univ. J. Mater. Sci.1, 180-200], we analyzed the dynamics of gas transport in the reactor with account nonlinearity of dynamics and rotation of keeper of substrate with the substrate. Based on the analysis, we formulated recommendation to optimize regime of rotation to increase homogeneity of properties of epitaxial layer.

Pankratov, E. L.; Bulaeva, E. A.

2014-06-01

190

Nucleation transitions in undercooled Cu70Co30 immiscible alloy  

NASA Astrophysics Data System (ADS)

High temperature differential scanning calorimetry (DSC) is applied to undercool and crystallize melts of a Cu70Co30 alloy into the metastable miscibility gap. The kinetic prefactor ? and the activation energy ?G* of the nucleation rate are determined based on the statistical analysis within classical nucleation theory. The value of ? reaches 2.64 (0.21) × 1037 m-3 s-1, which is close to that of the value for homogenous nucleation and much larger than that of undercooled pure Co melts. The value of ?G* is estimated to be 67 (2.5) kBT which is also higher than that of undercooled pure Co melts. The nucleation of the crystallization of the Co-rich phase is governed by homogeneous nucleation or conditions that are indistinguishable from homogeneous nucleation and the Cu-rich liquid phase effectively prevents the occurrence of heterogeneous nucleation for the nucleation of the Co-rich phase in the liquid-phase separated Cu70Co30 alloy. The results indicate that nucleation of the crystalline phase is sensitively dependent on the metastable binodal, which modifies the nucleation boundary conditions, leading to an effective transition of the dominant nucleation mechanism that depends critically on the vicinity to the metastable miscibility gap.

Zhang, Yikun; Simon, Christian; Volkmann, Thomas; Kolbe, Matthias; Herlach, Dieter; Wilde, Gerhard

2014-07-01

191

Characterizing protein crystal nucleation  

NASA Astrophysics Data System (ADS)

We developed an experimental microfluidic based technique to measure the nucleation rates and successfully applied the technique to measure nucleation rates of lysozyme crystals. The technique involves counting the number of samples which do not have crystals as a function of time. Under the assumption that nucleation is a Poisson process, the fraction of samples with no crystals decays exponentially with the decay constant proportional to nucleation rate and volume of the sample. Since nucleation is a random and rare event, one needs to perform measurements on large number of samples to obtain good statistics. Microfluidics offers the solution of producing large number of samples at minimal material consumption. Hence, we developed a microfluidic method and measured nucleation rates of lysozyme crystals in supersaturated protein drops, each with volume of ˜ 1 nL. Classical Nucleation Theory (CNT) describes the kinetics of nucleation and predicts the functional form of nucleation rate in terms of the thermodynamic quantities involved, such as supersaturation, temperature, etc. We analyzed the measured nucleation rates in the context of CNT and obtained the activation energy and the kinetic pre-factor characterizing the nucleation process. One conclusion is that heterogeneous nucleation dominates crystallization. We report preliminary studies on selective enhancement of nucleation in one of the crystal polymorprhs of lysozyme (spherulite) using amorphous mesoporous bioactive gel-glass te{naomi06, naomi08}, CaO.P 2O5.SiO2 (known as bio-glass) with 2-10 nm pore-size diameter distribution. The pores act as heterogeneous nucleation centers and claimed to enhance the nucleation rates by molecular confinement. The measured kinetic profiles of crystal fraction of spherulites indicate that the crystallization of spherulites may be proceeding via secondary nucleation pathways.

Akella, Sathish V.

192

Interaction terms in gas-solid two-phase flows  

NASA Technical Reports Server (NTRS)

From both experimental data and theoretical results of the two-phase flow, the complete expression of the interaction force between a gas and solid particles at low Reynolds number flow is obtained. The interaction force contains two terms: one is proportional to the difference between the velocities of the gas and the solid particle with a coefficient as a function of volume fraction Z and the other is proportional to the product of the total pressure of the mixture and the gradient of solid volume fraction. The second term is new. When Z tends to 0, the completion expression of interaction force reduces to the well-known Stokes formula.

Pai, S. I.; Hsieh, T.

1973-01-01

193

Igniting homogeneous nucleation  

Microsoft Academic Search

Transient homogeneous nucleation is studied in the limit of large critical sizes. Starting from pure monomers, three eras of transient nucleation are characterized in the classic Becker-Döring kinetic equations with two different models of discrete diffusivity: the classic Turnbull-Fisher formula and an expression describing thermally driven growth of the nucleus. The latter diffusivity yields time lags for nucleation which are

J. C. Neu; L. L. Bonilla; A. Carpio

2005-01-01

194

Impact of nuclear irradiation on helium bubble nucleation at interfaces in liquid metals coupled to permeation through stainless steels  

E-print Network

The impact of nucleating gas bubbles in the form of a dispersed gas phase on hydrogen isotope permeation at interfaces between liquid metals, like LLE, and structural materials, like stainless steel, has been studied. Liquid metal to structural material interfaces involving surfaces, may lower the nucleation barrier promoting bubble nucleation at active sites. Hence, hydrogen isotope absorption into gas bubbles modelling and control at interfaces may have a capital importance regarding design, operation and safety. He bubbles as a permeation barrier principle is analysed showing a significant impact on hydrogen isotope permeation, which may have a significant effect on liquid metal systems, e.g., tritium extraction systems. Liquid metals like LLE under nuclear irradiation in, e.g., breeding blankets of a nuclear fusion reactor would generate tritium which is to be extracted and recirculated as fuel. At the same time that tritium is bred, helium is also generated and may precipitate in the form of nano bubbles...

Fradera, Jorge

2013-01-01

195

Carbon Dioxide Separation from Flue Gas by Phase Enhanced Absorption  

SciTech Connect

A new process, phase enhanced absorption, was invented. The method is carried out in an absorber, where a liquid carrier (aqueous solution), an organic mixture (or organic compound), and a gas mixture containing a gas to be absorbed are introduced from an inlet. Since the organic mixture is immiscible or at least partially immiscible with the liquid carrier, the organic mixture forms a layer or small parcels between the liquid carrier and the gas mixture. The organic mixture in the absorber improves mass transfer efficiency of the system and increases the absorption rate of the gas. The organic mixture serves as a transportation media. The gas is finally accumulated in the liquid carrier as in a conventional gas-liquid absorption system. The presence of the organic layer does not hinder the regeneration of the liquid carrier or recovery of the gas because the organic layer is removed by a settler after the absorption process is completed. In another aspect, the system exhibited increased gas-liquid separation efficiency, thereby reducing the costs of operation and maintenance. Our study focused on the search of the organic layer or transportation layer to enhance the absorption rate of carbon dioxide. The following systems were studied, (1) CO{sub 2}-water system and CO{sub 2}-water-organic layer system; (2) CO{sub 2}-Potassium Carbonate aqueous solution system and CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system. CO{sub 2}-water and CO{sub 2}-Potassium Carbonate systems are the traditional gas-liquid absorption processes. The CO{sub 2}-water-organic layer and CO{sub 2}-Potassium Carbonate-organic layer systems are the novel absorption processes, phase enhanced absorption. As we mentioned early, organic layer (transportation layer phase) is used for the increase of absorption rate. Our study showed that the absorption rate can be increased by adding the organic layer. However, the enhanced factor is highly depended on the liquid mass transfer coefficient.

Liang Hu

2006-06-30

196

Gas-liquid chromatography with a volatile "stationary" liquid phase.  

PubMed

A unique type of gas-liquid chromatography is described in which both mobile and "stationary" phases are composed of synthetic mixtures of helium and carbon dioxide. At temperatures below the critical point of the binary mixture and pressures above the vapor pressure of pure liquid carbon dioxide, helium and carbon dioxide can form two immiscible phases over extended composition ranges. A binary vapor phase enriched in helium can act as the mobile phase for chromatographic separations, whereas a CO2-rich liquid in equilibrium with the vapor phase, but condensed on the column wall, can act as a pseudostationary phase. Several examples of chromatographic separations obtained in "empty" capillary columns with no ordinary stationary liquid phase illustrate the range of conditions that produce such separations. In addition, several experiments are reported that confirm the proposed two-phase hypothesis. The possible consequences of the observed chromatographic phenomenon in the field of supercritical fluid chromatography with helium headspace carbon dioxide are discussed. PMID:12033313

Wells, P S; Zhou, S; Parcher, J F

2002-05-01

197

Chemistry inside molecular containers in the gas phase  

NASA Astrophysics Data System (ADS)

Inner-phase chemical reactions of guest molecules encapsulated in a macromolecular cavity give fundamental insight into the relative stabilization of transition states by the surrounding walls of the host, thereby modelling the situation of substrates in enzymatic binding pockets. Although in solution several examples of inner-phase reactions are known, the use of cucurbiturils as macrocyclic hosts and bicyclic azoalkanes as guests has now enabled a systematic mass spectrometric investigation of inner-phase reactions in the gas phase, where typically the supply of thermal energy results in dissociation of the supramolecular host-guest assembly. The results reveal a sensitive interplay in which attractive and repulsive van der Waals interactions between the differently sized hosts and guests need to be balanced with a constrictive binding to allow thermally activated chemical reactions to compete with dissociation. The results are important for the understanding of supramolecular reactivity and have implications for catalysis.

Lee, Tung-Chun; Kalenius, Elina; Lazar, Alexandra I.; Assaf, Khaleel I.; Kuhnert, Nikolai; Grün, Christian H.; Jänis, Janne; Scherman, Oren A.; Nau, Werner M.

2013-05-01

198

Stimulation of ice nucleation by marine diatoms  

NASA Astrophysics Data System (ADS)

Atmospheric aerosol particles serve as nuclei for ice-crystal formation. As such, these particles are critical to the generation of cirrus clouds, which form from gas and liquid water. Atmospheric aerosols also initiate ice formation in warmer, mixed-phase clouds, where ice crystals coexist with aqueous droplets. Biogenic aerosol particles of terrestrial origin, including bacteria and pollen, can act as ice nuclei. Whether biogenic particles of marine origin also act as ice nuclei has remained uncertain. We exposed the cosmopolitan planktonic diatom species Thalassiosira pseudonana to water vapour and supercooled aqueous sodium chloride under typical tropospheric conditions conducive to cirrus-cloud formation. Ice nucleation was determined using a controlled vapour cooling-stage microscope system. Under all conditions, diatoms initiated ice formation. The presence of diatoms in water increased the temperature for ice formation up to 13K, and in aqueous sodium chloride, ice formed at temperatures up to 30K higher than when diatoms were not present. In addition, diatoms initiated ice formation from water vapour at relative humidities as low as 65%. The rate of ice nucleation was rapid and independent of surface area. We suggest that marine biogenic particles such as diatoms help explain high values and seasonal variations in ice-nuclei concentrations in subpolar regions.

Knopf, D. A.; Alpert, P. A.; Wang, B.; Aller, J. Y.

2011-02-01

199

Gas-phase reactivity of ruthenium carbonyl cluster anions.  

PubMed

Partially-ligated anionic ruthenium carbonyl clusters react with alkenes, arenes, and alkanes in the gas phase; the products undergo extensive C-H activation and lose dihydrogen and carbon monoxide under collision-induced dissociation conditions. Triethylsilane and phenylsilane are also reactive towards the unsaturated clusters, and oxygen was shown to rapidly break down the cluster core by oxidative cleavage of the metal-metal bonds. These qualitative gas-phase reactivity studies were conducted using an easily-installed and inexpensive modification of a commercial electrospray ionization mass spectrometer. Interpretation of the large amounts of data generated in these studies is made relatively straightforward by employing energy-dependent electrospray ionization mass spectrometry (EDESI-MS). PMID:19185511

Henderson, Matthew A; Kwok, Samantha; McIndoe, J Scott

2009-04-01

200

Studies of Nucleation and Growth, Specific Heat and Viscosity of Undercooled Melts of Quasicrystals and Polytetrehedral-Phase-Forming Alloys  

NASA Technical Reports Server (NTRS)

By investigating the properties of quasicrystals and quasicrystal-forming liquid alloys, we may determine the role of ordering of the liquid phase in the formation of quasicrystals, leading to a better fundamental understanding of both the quasicrystal and the liquid. A quasicrystal is solid characterized by a symmetric but non-periodic arrangement of atoms, usually in the form of an icosahedron (12 atoms, 20 triangular faces). It is theorized that the short-range order in liquids takes this same form. The degree of ordering depends on the temperature of the liquid, and affects many of the liquid s properties, including specific heat, viscosity, and electrical resistivity. The MSFC role in this project includes solidification studies, phase diagram determination, and thermophysical property measurements on the liquid quasicrystal-forming alloys, all by electrostatic levitation (ESL). The viscosity of liquid quasicrystal-forming alloys is measured by the oscillating drop method, both in the stable and undercooled liquid state. The specific heat of solid, undercooled liquid, and stable liquid are measured by the radiative cooling rate of the droplets.

2003-01-01

201

Gas phase fractionation method using porous ceramic membrane  

DOEpatents

Flaw-free porous ceramic membranes fabricated from metal sols and coated onto a porous support are advantageously used in gas phase fractionation methods. Mean pore diameters of less than 40 .ANG., preferably 5-20 .ANG. and most preferably about 15 .ANG., are permeable at lower pressures than existing membranes. Condensation of gases in small pores and non-Knudsen membrane transport mechanisms are employed to facilitate and increase membrane permeability and permselectivity.

Peterson, Reid A. (Madison, WI); Hill, Jr., Charles G. (Madison, WI); Anderson, Marc A. (Madison, WI)

1996-01-01

202

Two-phase flow characteristics in gas–liquid microreactors  

Microsoft Academic Search

Multiphase chemical microreactors require a detailed knowledge of the flow conditions inside the reaction system. This paper reports flow visualization measurements of the two-phase gas–liquid flow pattern and the liquid velocity distribution inside liquid plugs of an intermittent flow. Rectangular cross-section silicon microchannels with hydraulic diameters between 187.5 and 218?m are fabricated. Laser Induced Fluorescence (LIF) is used to determine

Severin Waelchli; Philipp Rudolf von Rohr

2006-01-01

203

Gas-phase reactivity of ruthenium carbonyl cluster anions  

Microsoft Academic Search

Partially-ligated anionic ruthenium carbonyl clusters react with alkenes, arenes, and alkanes in the gas phase; the products\\u000a undergo extensive C-H activation and lose dihydrogen and carbon monoxide under collision-induced dissociation conditions.\\u000a Triethylsilane and phenylsilane are also reactive towards the unsaturated clusters, and oxygen was shown to rapidly break\\u000a down the cluster core by oxidative cleavage of the metal-metal bonds. These

Matthew A. Henderson; Samantha Kwok; J. Scott McIndoe

2009-01-01

204

Gas-phase photolysis of phorate, a phosphorothioate insecticide  

Microsoft Academic Search

Novel methods are described for determining atmospheric photolysis rates for the moderately volatile pesticide, phorate. The gas-phase sunlight photolysis of this substance was determined in three test systems which include: (1) 3-L borosilicate flasks exposed to sunlight and laboratory solar simulation, (2) 100-L Tedlar sunlight exposed air sample bags, and (3) 12,800-L Tedlar sunlight exposed chamber studies using a photochemically

Vincent R. Hebert; Jason D. Geddes; Joy Mendosa; Glenn C. Miller

1998-01-01

205

Photodissociation pathways of gas-phase photoactive yellow protein chromophores  

NASA Astrophysics Data System (ADS)

The absorption dynamics of two model chromophores of the photoactive yellow protein were studied in gas-phase experiments. Using different time-resolving techniques with an overall sensitivity ranging from seconds down to a few nanoseconds, complex dynamics were revealed for the p -coumaric acid anion, involving both fragmentation and electron detachment as possible photoresponse channels. For the trans-thiophenyl- p -coumarate model, despite its more complex molecular structure, simpler decay dynamics showing only fragmentation were observed.

Lammich, Lutz; Rajput, Jyoti; Andersen, Lars H.

2008-11-01

206

The nucleoside uridine isolated in the gas phase.  

PubMed

Herein we present the first experimental observation of the isolated nucleoside uridine, placed in the gas phase by laser ablation and characterized by Fourier transform (FT) microwave techniques. Free from the bulk effects of their native environments, anti/C2'-endo-g+ conformation has been revealed as the most stable form of uridine. Intramolecular hydrogen bonds involving uracil and ribose moieties have been found to play an important role in the stabilization of the nucleoside. PMID:25683559

Peña, Isabel; Cabezas, Carlos; Alonso, José L

2015-03-01

207

Gas phase photocatalytic removal of toluene effluents on sulfated titania  

Microsoft Academic Search

Photocatalytic removal of toluene in the gas phase was carried out over UV-illuminated sulfated titania materials in a cylinder-like continuous reactor. A series of SO42?–TiO2 samples was obtained from the addition of H2SO4 on an amorphous titanium hydroxide gel synthesized according to a classical sol–gel procedure. The wide variety of materials led to varying photocatalytic behaviors depending strongly on the

Elodie Barraud; Florence Bosc; David Edwards; Nicolas Keller; Valérie Keller

2005-01-01

208

Discrimination of gas-phase emissions from building material samples by combining two gas-sensor arrays  

E-print Network

Discrimination of gas-phase emissions from building material samples by combining two gas.ramalho@cstb.fr Keywords: Gas sensor array, Building material, Discrimination, Feature extraction Introduction As part, experiments have been performed to assess the discrimination power of two gas-sensor systems as regards

Paris-Sud XI, Université de

209

Gas phase basicities of polyfunctional molecules. Part 3: Amino acids.  

PubMed

The present article is the third part of a general overview of the gas-phase protonation thermochemistry of polyfunctional molecules (first part: Mass Spectrom. Rev., 2007, 26:775-835, second part: Mass Spectrom. Rev., 2011, in press). This review is devoted to the 20 proteinogenic amino acids and is divided in two parts. In the first one, the experimental data obtained during the last 30 years using the equilibrium, thermokinetic and kinetic methods are presented. A general re-assignment of the values originating from these various experiments has been done on the basis of the commonly accepted Hunter & Lias 1998 gas-phase basicity scale in order to provide an homogeneous set of data. In the second part, theoretical investigations on gaseous neutral and protonated amino acids are reviewed. Conformational landscapes of both types of species were examined in order to provide theoretical protonation thermochemistry based on the truly identified most stable conformers. Proton affinities computed at the presently highest levels of theory (i.e. composite methods such as Gn procedures) are presented. Estimates of thermochemical parameters calculated using a Boltzmann distribution of conformers at 298K are also included. Finally, comparison between experiment and theory is discussed and a set of evaluated proton affinities, gas-phase basicities and protonation entropies is proposed. PMID:22611554

Bouchoux, Guy

2012-01-01

210

Phase behavior of glycol in gas pipeline calculated  

SciTech Connect

Transportation of wet, CO{sub 2}-containing gases in pipelines requires special measures to prevent corrosion of the pipe wall. A relatively new option uses injection of glycol, the presence of which in the water phase mitigates corrosion. A method has been developed for calculating the phase behavior of glycol in such wet CO{sub 2} pipelines. Composition of the glycol-water condensate in the pipeline is one essential in determination of the corrosion rate. The effect of natural-gas condensate on the mass transfer of glycol and water between liquid glycol-water at the bottom of the pipeline and the gas phase is approached by means of two dispersion criteria. The composition of glycol-water is shown for the various cases considered for the various cases considered for the operation of the 66-km, 36-in. trunklines between the Troll platform of the Norwegian coast and the offshore processing plant on the Troll natural-gas pipeline system.

Lammers, J.N.J.J. (Shell Research B.V., Amsterdam (NL))

1991-04-15

211

Nucleation and growth of Ag nanoparticles on amorphous carbon surface from vapor phase formed by vacuum evaporation  

NASA Astrophysics Data System (ADS)

We present the results of experimental study of Ag nanoparticle arrays on thin film of amorphous carbon. The arrays were formed by means of vapor phase deposition on non-heated substrate. The investigation was carried out using TEM technique. It has been found that the size of the particles and their surface density significantly depend on the amount of condensing substance. In particular, increasing the portion of evaporating Ag material from 5.1 to 47.5 mg results in drastic reduction of surface density of the particles from ~8,000 to ~40 µm-2, whereas the predominant particle size changes from ~7 to ~60 nm. We present phenomenological description of the process: directed flow of silver atoms to growing Ag particles takes place during condensation.

Gromov, Dmitry G.; Pavlova, Lydia M.; Savitsky, Andrey I.; Trifonov, Alexey Yu.

2015-03-01

212

Nucleation of earthquakes and its implication to precursors  

NASA Astrophysics Data System (ADS)

The recent argument about nucleation phase of earthquakes reminds us to completely study the concept of earthquake nucleation. The original meaning of nucleation includes concentration, nucleation and initiation of the eruptive processes. Thus, it is needed to discuss how to exactly translate the word “nucleation” into Chinese in different fields. The basic concept of earthquake nucleation refers to microcrack concentration in rock. It causes local weakening and instability of the rock. The narrow sense of nucleation theory of friction constitutive is significant in friction of fault surfaces, but should not abuse everywhere unconditionally. In terms of thermodynamics, nucleation actually means the variety processes of multiple state parameters of rock. The nucleation is a project that covers multiple courses. In this paper, the studies of damage theory, fracture, earthquake rupture dynamics and constitutive of friction and their implication to earthquake nucleation are remarked. The recently developments are introduced, including the influence of tectonic on the earthquake nucleation process, the method of measuring medium anisotropy, especially shear wave splitting led by concentration and orientation of microcracks, and the experimental study of remote sensing of infrared and microwave radiation related to the nucleation, etc. This paper also discusses the characteristic of large earthquake nucleation, and the implication of above studies to precursors of strong earthquakes.

Li, Shi-Yu; Teng, Chun-Kai; Lu, Zhen-Ye; Liu, Xiao-Hong; Liu, Qi-Liang; He, Xue-Song

2000-03-01

213

Carbon Dioxide Separation from Flue Gas by Phase Enhanced Absorption  

SciTech Connect

A new process, phase enhanced absorption, was invented. The method is carried out in an absorber, where a liquid carrier (aqueous solution), an organic mixture (or organic compound), and a gas mixture containing a gas to be absorbed are introduced from an inlet. Since the organic mixture is immiscible or at least partially immiscible with the liquid carrier, the organic mixture forms a layer or small parcels between the liquid carrier and the gas mixture. The organic mixture in the absorber improves mass transfer efficiency of the system and increases the absorption rate of the gas. The organic mixture serves as a transportation media. The gas is finally accumulated in the liquid carrier as in a conventional gas-liquid absorption system. The presence of the organic layer does not hinder the regeneration of the liquid carrier or recovery of the gas because the organic layer is removed by a settler after the absorption process is completed. In another aspect, the system exhibited increased gas-liquid separation efficiency, thereby reducing the costs of operation and maintenance. Our study focused on the search of the organic layer or transportation layer to enhance the absorption rate of carbon dioxide. The following systems were studied, (1) CO{sub 2}-water system and CO{sub 2}-water-organic layer system; (2) CO{sub 2}-Potassium Carbonate aqueous solution system and CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system. CO{sub 2}-water and CO{sub 2}-Potassium Carbonate systems are the traditional gas-liquid absorption processes. The CO{sub 2}-water-organic layer and CO{sub 2}-Potassium Carbonate-organic layer systems are the novel absorption processes, phase enhanced absorption. As we mentioned early, organic layer is used for the increase of absorption rate, and plays the role of transportation of CO{sub 2}. Our study showed that the absorption rate can be increased by adding the organic layer. However, the enhanced factor is highly depended on the liquid mass transfer coefficients for the CO{sub 2}-water-organic layer system. For the CO{sub 2}-Potassium Carbonate aqueous solution-organic layer system, the enhanced factor is not only dependent on the liquid mass transfer coefficients, but also the chemical reaction rates.

Tim Fout

2007-06-30

214

The partitioning of ketones between the gas and aqueous phases  

NASA Astrophysics Data System (ADS)

Most ketones are not significantly hydrated; they therefore retain their chromophore and they could be photolytically degraded in solution yielding a variety of products including carboxylic acids, aldehydes and radicals. It is difficult to accurately model the partitioning of ketones between the gas phase and aqueous phase because of the lack suitable estimates of the Henry's Law constants; consequently the fate and environmental effects of ketones cannot be confidently predicted. Here we report the experimental determination of the Henry's Law constants of a series of ketones that has yielded a simple straight line equation to predict the Henry's Law constants of simple aliphatic ketones: log H ? =0.23?? ? + 1.51; where H ? is the effective Henry's Law constant (M atm -1, and ?? ? is the Taft polar substituents constants. The results for 25°C are (M atm -1) CH 3COCH 3, 32; C 6H 5COCH 3, 110; CH 2ClCOCH 3, 59; CH 3COCOCH 3, 74; CF 3COCH 3, 138. Acetophenone appears to have an abnormally high H ?. Most low molecular weight aliphatic ketones are predicted to characterized by H ??30 M atm -1 and therefore they are expected to be found in the aqueous phase at concentrations of ?5 - 0.5 ?M (given a typical gas-phase concentration range of 1-10 ppbv). The expected rate of decomposition of ketones due to photolysis in hydrometers is briefly discussed.

Betterton, Eric A.

215

H/D Exchange Levels of Shape-Resolved Cytochrome c Conformers in the Gas Phase  

E-print Network

H/D Exchange Levels of Shape-Resolved Cytochrome c Conformers in the Gas Phase Stephen J. Valentine) in the gas phase are examined by simultaneous ion-mobility and hydrogen-deuterium exchange measurements with the idea that compact structures protect some hydrogens in the gas phase. Many sites that rapidly exchange

Clemmer, David E.

216

Revision of the thermodynamics of the proton in gas phase.  

PubMed

Proton transfer is ubiquitous in various physical/chemical processes, and the accurate determination of the thermodynamic parameters of the proton in the gas phase is useful for understanding and describing such reactions. However, the thermodynamic parameters of such a proton are usually determined by assuming the proton as a classical particle whatever the temperature. The reason for such an assumption is that the entropy of the quantum proton is not always soluble analytically at all temperatures. Thereby, we addressed this matter using a robust and reliable self-consistent iterative procedure based on the Fermi-Dirac formalism. As a result, the free proton gas can be assumed to be classical for temperatures higher than 200 K. However, it is worth mentioning that quantum effects on the gas phase proton motion are really significant at low temperatures (T ? 120 K). Although the proton behaves as a classical particle at high temperatures, we strongly recommend the use of quantum results at all temperatures, for the integrated heat capacity and the Gibbs free energy change. Therefore, on the basis of the thermochemical convention that ignores the proton spin, we recommend the following revised values for the integrated heat capacity and the Gibbs free energy change of the proton in gas phase and, at the standard pressure (1 bar): ?H0?T = 6.1398 kJ mol(-1) and ?G0?T = -26.3424 kJ mol(-1). Finally, it is important noting that the little change of the pressure from 1 bar to 1 atm affects notably the entropy and the Gibbs free energy change of the proton. PMID:25338234

Fifen, Jean Jules; Dhaouadi, Zoubeida; Nsangou, Mama

2014-11-20

217

Specific, trace gas induced phase transition in copper(II)oxide for highly selective gas sensing  

NASA Astrophysics Data System (ADS)

Here, we present results on the investigation of the percolation phase transition in copper(II)oxide (CuO) and show how it may be used to determine trace gas concentrations. This approach provides a highly selective sensing mechanism for the detection of hydrogen sulfide even in oxygen depleted atmospheres. In real-world applications, this scenario is encountered in biogas plants and natural gas facilities, where reliable H2S sensing and filtering are important because of the destructive effects H2S has on machinery. As opposed to gas detection via standard metal-oxide reaction routes, the percolation dynamics are demonstrated to be independent of the surface morphology in accordance with the universality of phase transitions. The sensing behavior of ink-jet printed CuO layers was tested for a large set of parameters including layer temperature, hydrogen sulfide (H2S) and oxygen concentration, as well as the sensitivity towards other gas species. The electrical percolation of the sensing layer is heralded by a dramatic drop in the overall resistivity of the CuO layer for temperatures below 200 °C. The observed percolation phenomena in this temperature regime are unique to H2S even in comparison with related volatile thio-compounds making the sensing mechanism highly selective. At elevated temperatures above 300 °C, the phase transition does not occur. This enables two distinct operational modes which are tunable via the sensor temperature and also allows for resetting the sensing layer after an electrical breakthrough.

Kneer, J.; Wöllenstein, J.; Palzer, S.

2014-08-01

218

Gas phase oxidation downstream of a catalytic combustor  

NASA Technical Reports Server (NTRS)

Effect of the length available for gas-phase reactions downstream of the catalytic reactor on the emission of CO and unburned hydrocarbons was investigated. A premixed, prevaporized propane/air feed to a 12/cm/diameter catalytic/reactor test section was used. The catalytic reactor was made of four 2.5 cm long monolithic catalyst elements. Four water cooled gas sampling probes were located at positions between 0 and 22 cm downstream of the catalytic reactor. Measurements of unburned hydrocarbon, CO, and CO2 were made. Tests were performed with an inlet air temperature of 800 K, a reference velocity of 10 m/s, pressures of 3 and 600,000 Pa, and fuel air equivalence ratios of 0.14 to 0.24. For very lean mixtures, hydrocarbon emissions were high and CO continued to be formed downstream of the catalytic reactor. At the highest equivalence ratios tested, hydrocarbon levels were much lower and CO was oxidized to CO2 in the gas phase downstream. To achieve acceptable emissions, a downstream region several times longer than the catalytic reactor could be required.

Tien, J. S.; Anderson, D. N.

1979-01-01

219

Ice-Nucleating Bacteria  

NASA Astrophysics Data System (ADS)

Since the discovery of ice-nucleating bacteria in 1974 by Maki et al., a large number of studies on the biological characteristics, ice-nucleating substance, ice nucleation gene and frost damage etc. of the bacteria have been carried out. Ice-nucleating bacteria can cause the freezing of water at relatively warm temperature (-2.3°C). Tween 20 was good substrates for ice-nucleating activity of Pseudomonas fluorescens KUIN-1. Major fatty acids of Isolate (Pseudomonas fluorescens) W-11 grown at 30°C were palmitic, cis-9-hexadecenoic and cis-11-octadecenoic which amounted to 90% of the total fatty acids. Sequence analysis shows that an ice nucleation gene from Pseudomonas fluorescens is related to the gene of Pseudomonas syringae.

Obata, Hitoshi

220

Phase transition or Maxwell's demon in Granular gas?  

E-print Network

Dynamics of vibro-fluidised granular gas is investigated experimentally using the transfer of grains from a compartment through a horizontal slit at a given height h . It is demonstrated that the transfer rate j varies linearly with the grain number N in the box when N remains small; however j(N) becomes strongly non linear as soon as the number n of layers is larger than 0.3; dj/dN becomes negative for n>0.4.It is found also that the maximum of j(N) increases slightly with the acceleration af_ of the vibration which excites the granular gas. Using dynamical system theory, dynamics equations are written, and a critical bifurcation is found, which explains the existence of a condensation and of a phase transition. This explains how the pseudo " Maxwell's demon" works in granular gases. This experiments contradicts recent modeling . Pacs # : 5.40 ; 45.70 ; 62.20 ; 83.70.Fn

P. Jean; H. Bellenger; P. Burban; L. Ponson; P. Evesque

2005-06-23

221

Microcanonical molecular simulations of methane hydrate nucleation and growth: evidence that direct nucleation to sI hydrate is among the multiple nucleation pathways.  

PubMed

The results of six high-precision constant energy molecular dynamics (MD) simulations initiated from methane-water systems equilibrated at 80 MPa and 250 K indicate that methane hydrates can nucleate via multiple pathways. Five trajectories nucleate to an amorphous solid. One trajectory nucleates to a structure-I hydrate template with long-range order which spans the simulation box across periodic boundaries despite the presence of several defects. While experimental and simulation data for hydrate nucleation with different time- and length-scales suggest that there may exist multiple pathways for nucleation, including metastable intermediates and the direct formation of the globally-stable phase, this work provides the most compelling evidence that direct formation to the globally stable crystalline phase is one of the multiple pathways available for hydrate nucleation. PMID:25743115

Zhang, Zhengcai; Walsh, Matthew R; Guo, Guang-Jun

2015-04-14

222

Homogeneous Nucleation in Inhomogeneous Media I: Nucleation in a Temperature Gradient  

E-print Network

We introduce a general formalism to analyze nucleation phenomena in inhomogeneous media which considers the influence of the metastable phase, which is treated as a heat bath in which clusters are embedded, in the dynamics of the nucleation process. A kinetic equation for the evolution of the probability density of the clusters, taking into account possible inhomogeneities in the bath, is derived using mesoscopic nonequilibrium thermodynamics. From it, we obtain the nucleation rate and analyze the role played by the metastable phase in the process. We discuss in particular condensation and polymer crystallization in a temperature gradient.

D. Reguera; J. M. Rubi

2003-09-08

223

Experiments on Nucleation in Different Flow Regimes  

NASA Technical Reports Server (NTRS)

The vast majority of metallic engineering materials are solidified from the liquid phase. Understanding the solidification process is essential to control microstructure, which in turn, determines the properties of materials. The genesis of solidification is nucleation, where the first stable solid forms from the liquid phase. Nucleation kinetics determine the degree of undercooling and phase selection. As such, it is important to understand nucleation phenomena in order to control solidification or glass formation in metals and alloys. Early experiments in nucleation kinetics were accomplished by droplet dispersion methods [1-6]. Dilitometry was used by Turnbull and others, and more recently differential thermal analysis and differential scanning calorimetry have been used for kinetic studies. These techniques have enjoyed success; however, there are difficulties with these experiments. Since materials are dispersed in a medium, the character of the emulsion/metal interface affects the nucleation behavior. Statistics are derived from the large number of particles observed in a single experiment, but dispersions have a finite size distribution which adds to the uncertainty of the kinetic determinations. Even though temperature can be controlled quite well before the onset of nucleation, the release of the latent heat of fusion during nucleation of particles complicates the assumption of isothermality during these experiments. Containerless processing has enabled another approach to the study of nucleation kinetics [7]. With levitation techniques it is possible to undercool one sample to nucleation repeatedly in a controlled manner, such that the statistics of the nucleation process can be derived from multiple experiments on a single sample. The authors have fully developed the analysis of nucleation experiments on single samples following the suggestions of Skripov [8]. The advantage of these experiments is that the samples are directly observable. The nucleation temperature can be measured by noncontact optical pyrometry, the mass of the sample is known, and post processing analysis can be conducted on the sample. The disadvantages are that temperature measurement must have exceptionally high precision, and it is not possible to isolate specific heterogeneous sites as in droplet dispersions.

Bayuzick, Robert J.

1999-01-01

224

The solar system/interstellar medium connection - Gas phase abundances  

NASA Technical Reports Server (NTRS)

Gas-phase abundances in the outer solar system are presented as diagnostics of the interstellar medium at the time of the solar system formation, some 4.55 billion years ago. Possible influences of the thermal and chemical histories of the primitive solar nebula and of the processes which led to the formation and evolution of the outer planets and comets on the elemental and molecular composition of the primordial matter are outlined. The major components of the atmospheres of the outer planets and of the comae of comets are identified, and the cosmogonical and cosmological implications are discussed.

Lutz, Barry L.

1987-01-01

225

Gas-phase chemiluminescent reactions of ozone with monoterpenes  

NASA Astrophysics Data System (ADS)

Chemiluminescent reactions of ozone with monoterpenes such as linallol, geraniol, d-limonene and ?-pinene have been studied in the gas phase at low pressures. Methylglyoxal phosphorescence has been observed in the first two reactions. Emissions from HCHO( 1A 2) and glyoxal ( 3A u) are observed in the reaction of ozone with d-limonene and formation of excited glyoxal is found to be first order in ozone. The reaction of ozone with ?-pinene gives rise to emission from a ?-dicarbonyl compound and this is found to be first order in ozone. The mechanisms for the formation of excited species are proposed.

Arora, P. K.; Chatha, J. P. S.; Vohra, K. G.

1983-08-01

226

The shape of ibuprofen in the gas phase.  

PubMed

Ibuprofen's pain-relieving properties arise from its ability to physically block the active site of an enzyme, thus making its structural and conformational properties highly interesting. We here present a conformer-selective high-resolution broadband rotational spectroscopy study of gas-phase ibuprofen. The interpretation of the spectroscopic results is supported by quantum-chemical calculations. We identify four low-energy conformers that differ in the structural arrangement of the isobutyl moiety with respect to the remainder of the molecule. While the isobutyl group shows high structural flexibility - resulting in distinct low-energy conformers - the propanoic acid group favors a stable arrangement. PMID:25582126

Betz, Thomas; Zinn, Sabrina; Schnell, Melanie

2015-01-28

227

Gas Phase Study of C+ Reactions of Interstellar Relevance  

NASA Astrophysics Data System (ADS)

The current uncertainty in many reaction rate constants causes difficulties in providing satisfactory models of interstellar chemistry. Here we present new measurements of the rate constants and product branching ratios for the gas phase reactions of C+ with NH3, CH4, O2, H2O, and C2H2, using the flowing afterglow-selected ion flow tube (FASIFT) technique. Results were obtained using two instruments that were separately calibrated and optimized; in addition, low ionization energies were used to ensure formation of ground-state C+, the purities of the neutral reactants were verified, and mass discrimination was minimized.

Martinez, Oscar, Jr.; Betts, Nicholas B.; Villano, Stephanie M.; Eyet, Nicole; Snow, Theodore P.; Bierbaum, Veronica M.

2008-10-01

228

Multiscale Aspects of Modeling Gas-Phase Nanoparticle Synthesis  

PubMed Central

Aerosol reactors are utilized to manufacture nanoparticles in industrially relevant quantities. The development, understanding and scale-up of aerosol reactors can be facilitated with models and computer simulations. This review aims to provide an overview of recent developments of models and simulations and discuss their interconnection in a multiscale approach. A short introduction of the various aerosol reactor types and gas-phase particle dynamics is presented as a background for the later discussion of the models and simulations. Models are presented with decreasing time and length scales in sections on continuum, mesoscale, molecular dynamics and quantum mechanics models. PMID:23729992

Buesser, B.; Gröhn, A.J.

2013-01-01

229

Nucleation of cBN on various substrate materials under high-pressure–high-temperature conditions  

Microsoft Academic Search

Whereas the low-pressure synthesis of diamond from the gas phase has become a well-established technology, equivalent low-pressure c-BN synthesis is not yet possible. So far, macroscopic crystalline c-BN powders can only be synthesized by high-pressure\\/high-temperature methods. For a successful low-pressure synthesis of c-BN, both nucleation and, subsequently, a continuous growth on appropriate solid substrate materials are required. It is shown

B Lux; W Kalss; R Haubner; T Taniguchi

1999-01-01

230

Experimental study of Gas Phase Formation and Evolution in Low fO2 Planetary Basalts.  

NASA Astrophysics Data System (ADS)

The existence of a gas phase in planetary basaltic magmas is demonstrated by the ubiquitous presence of vesicles in returned lunar samples and meteorites as well as basalts from Earth and Mars. Additionally, formation of the fine-grained glass bead deposits during eruption of lunar picritic glasses required a large gas-bubble volume (> 90%) at the time of eruption/fragmentation. Up to 100-200 ppm levels of H, S, Cl and F still remain as diffusion-loss profiles in individual lunar glass beads SIMS (1), and higher volatile concentrations occur in olivine melt inclusions (2). The composition and origin of such volcanic gases were investigated by experiments on a volatile (C-O-H-S-Cl-F)-bearing picritic glass composition as a function of fO2 near iron-wustite (IW). The C-O-H species dissolved in gas-saturated basaltic melt above IW-0.5 are carbonate, OH and H2O with 100 to 10,000 ppm H2O in the sample; below IW-0.5, the C-species present (Raman and FTIR) are Fe(CO)5 (iron pentacarbonyl) and lesser CH4 [3]. The change in melt speciation in part reflects a change in calculated speciation in the coexisting gas [4]. The carbon solubility in these experimental melts increases linearly with increasing pressure; the more oxidized glasses contain 32-620 ppm C for pressures of 98 to 980 MPa, the reduced glasses contain 8-240 ppm C for pressures between 36 and 900 MPa. Thus, the C solubility of the more reduced Fe-carbonyl and CH4 is about one-half that of carbonate at the same pressure, and indicates the carrying capacity for C in reduced (i.e., lunar) magmas is much lower than it is in present day terrestrial magmas. Varioles up to 200 um in diameter formed in some experiments with higher dissolved water contents (1%); they have radiating crystalline textures (olivine, glass and poorly crystallized graphite) initiated at a central nucleation site. A sharp peak in the variole Ramen spectra indicates methane as well as CO is released during variole formation and a reaction such as 2CO = C +CO2 formed the graphite. Several series of experiments on chips of low fO2 glass created at high pressure quantify S, Cl and F partitioning into the H2O-CO gas phase with decompression steps from 200 to 40 MPa. A gas formed with the first pressure drop, indicating melt supersaturation with CO and/or CH4; H2O and lesser amounts of S, Cl and F partitioned into the initial gas, and continued to do so with additional drops in pressure. The ubiquitous Fe-metal seen in lunar picritic glasses may form by graphite oxidation, but also may form by breakdown of Fe(CO)5 as the melt continues to saturate during ascent. [1] A. E. Saal et al.(2008) Nature 454, 192-195. [2] E. H. Hauri et al (2011) Science 333, 213 -215. [3] Wetzel, D., Rutherford, M.J. Jacobsen S.D., Hauri, E.H., and Saal, A.E., (submitted); Nature Geoscience Aug. 1, 2012. [4] Zhang, C. and Duan, Z. (2009) GCA, 73, 2089-2102.

Rutherford, M. J.; Wetzel, D. T.; Saal, A. E.; Hauri, E. H.

2012-12-01

231

Nucleation behavior during solidification of cast iron at high undercooling  

Microsoft Academic Search

During the solidification, of cast iron, a modest melt undercooling is a common observation, but the identity of the nucleation catalyst limiting the amount of undercooling has been elusive. In order to examine the influence of primary phases on the heterogeneous nucleation behavior of secondary phases in both hypoeutectic and hypereutectic cast irons, solidification catalysis experiments were carried out with

T. Mizoguchi; J. H. Perepezko

1997-01-01

232

Gas-Phase and Particle-Phase Reaction and Kinetics of Epoxydiols from Photooxidation of Isoprene  

NASA Astrophysics Data System (ADS)

The emission of isoprene from deciduous plants is estimated to be upwards of 500 Tg a year and plays an important role in tropospheric chemistry over large regions of the globe. Both laboratory and field measurements have found evidence of large amounts of isoprene derivatives in secondary organic aerosols (SOAs). SOA formation has been shown to be favored under low-NOx conditions, producing aerosols with high concentrations of tetrols, sulfate esters, and C5 repeating polymeric species. The exact gas phase chemical precursors of the organics found in these SOAs are still debated. Recently, it has been shown that under low-NOx conditions the photooxidation of isoprene will result in the formation of isoprene epoxydiols. We have studied the gas-phase, aerosol-phase, and liquid-phase reactivity of a number of alkane epoxydiols. Experiments on the production of epoxydiols from the photooxidation of isoprene and butadiene as well as the uptake of these species by aerosol seed particles were performed in the Caltech dual 28-m3 environmental chamber. The gas-phase loss of the epoxydiols by aerosol uptake was monitored by chemical ionization mass spectrometry along with the products of the photooxidation of the epoxydiols. The organic composition of aerosols from the uptake of epoxydiols as well as from the photooxidation of isoprene was determined by a number of mass spectrometry techniques from chamber filter samples. Finally, the products and kinetics of the liquid-phase acid hydrolysis of the epoxides was determined by NMR. The epoxydiols were found to be readily incorporated into acidic aerosols by reactive uptake as well as partitioning. The organic composition of the SOAs from uptake of epoxydiols or the photooxidation of isoprene by acidic seeds were found to be very similar to the products of the acidic hydrolysis of the epoxydiols consisting of tetrols, sulfate esters, and polymeric species.

Eddingsaas, N. C.; Chan, A. W.; Surratt, J. D.; Seinfeld, J.; Wennberg, P. O.

2009-12-01

233

Gas-phase Dissociation of homo-DNA Oligonucleotides  

NASA Astrophysics Data System (ADS)

Synthetic modified oligonucleotides are of interest for diagnostic and therapeutic applications, as their biological stability, pairing selectivity, and binding strength can be considerably increased by the incorporation of unnatural structural elements. Homo-DNA is an oligonucleotide homologue based on dideoxy-hexopyranosyl sugar moieties, which follows the Watson-Crick A-T and G-C base pairing system, but does not hybridize with complementary natural DNA and RNA. Homo-DNA has found application as a bioorthogonal element in templated chemistry applications. The gas-phase dissociation of homo-DNA has been investigated by ESI-MS/MS and MALDI-MS/MS, and mechanistic aspects of its gas-phase dissociation are discussed. Experiments revealed a charge state dependent preference for the loss of nucleobases, which are released either as neutrals or as anions. In contrast to DNA, nucleobase loss from homo-DNA was found to be decoupled from backbone cleavage, thus resulting in stable products. This renders an additional stage of ion activation necessary in order to generate sequence-defining fragment ions. Upon MS3 of the primary base-loss ion, homo-DNA was found to exhibit unspecific backbone dissociation resulting in a balanced distribution of all fragment ion series.

Stucki, Silvan R.; Désiron, Camille; Nyakas, Adrien; Marti, Simon; Leumann, Christian J.; Schürch, Stefan

2013-12-01

234

Electron scattering from gas-phase glycine molecules.  

PubMed

Low-energy electron collisions with gas-phase glycine molecules have been studied using the fixed-nuclei R-matrix method based on state-averaged complete-active-space self-consistent-field orbitals. A total of 40 electronic states of neutral glycine, including 3s and 3p Rydberg excited states, are included in the R-matrix model. A large peak is observed in the A(") partial elastic cross section around 3.4 eV, which originates from the pi( *) shape resonance. In addition, many sharp narrow peaks coming from core excited resonances are seen in the elastic and inelastic cross sections at energies above 5 eV. Although the effect of the Rydberg orbitals on the elastic cross section is insignificant, these orbitals are crucial to represent core excited resonances in the inelastic cross sections. In previous experiments on dissociative electron attachment to gas-phase glycine, noticeable product ion peaks have been observed at electron collision energies around 1-2 and 5-10 eV. The resonance positions obtained in our calculations are generally close to these experimental results. PMID:19045267

Tashiro, Motomichi

2008-10-28

235

Experimental signals of a nuclear liquid-gas phase transition  

NASA Astrophysics Data System (ADS)

The critical phenomenon of the nuclear liquid-gas phase transition has been investigated in the reactions 64Zn+64Zn, 64Ni+64Ni and 70Zn+70Zn at beam energy of 35 MeV/nucleon. Yields of fragments arising from fragmenting quasi-projectiles (QPs) with different neutron-proton asymmetries were analyzed within the framework of the Landau free energy approach. Fits to the free energy of fragments as a function of fragment asymmetry showed three minima, indicating the system to be in a regime of a first-order phase transition. The QP temperature estimates were extracted from the analysis of N=Z fragment data. Additionally, we make use of a recent method based on quantum fluctuations of fermions to derive temperatures and densities of selected QPs. Critical scaling of these observables is found for systems which differ in neutron to proton asymmetry. The derived critical exponent ? = 0.35 ± 0.01, belongs to the liquid-gas universality class.

Mabiala, J.; Bonasera, A.; Zheng, H.; McIntosh, A. B.; Kohley, Z.; Cammarata, P.; Hagel, K.; Heilborn, L.; May, L. W.; Raphelt, A.; Souliotis, G. A.; Zarrella, A.; Yennello, S. J.

2013-03-01

236

Nahoon: Time-dependent gas-phase chemical model  

NASA Astrophysics Data System (ADS)

Nahoon is a gas-phase chemical model that computes the chemical evolution in a 1D temperature and density structure. It uses chemical networks downloaded from the KInetic Database for Astrochemistry (KIDA) but the model can be adapted to any network. The program is written in Fortran 90 and uses the DLSODES (double precision) solver from the ODEPACK package to solve the coupled stiff differential equations. The solver computes the chemical evolution of gas-phase species at a fixed temperature and density and can be used in one dimension (1D) if a grid of temperature, density, and visual extinction is provided. Grains, both neutral and negatively charged, and electrons are considered as chemical species and their concentrations are computed at the same time as those of the other species. Nahoon contains a test to check the temperature range of the validity of the rate coefficients and avoid extrapolations outside this range. A test is also included to check for duplication of chemical reactions, defined over complementary ranges of temperature.

Wakelam, V.

2014-09-01

237

Gas-phase fragmentation analysis of nitro-fatty acids.  

PubMed

Nitro-fatty acids are electrophilic signaling mediators formed in increased amounts during inflammation by nitric oxide and nitrite-dependent redox reactions. A more rigorous characterization of endogenously-generated species requires additional understanding of their gas-phase induced fragmentation. Thus, collision induced dissociation (CID) of nitroalkane and nitroalkene groups in fatty acids were studied in the negative ion mode to provide mass spectrometric tools for their structural characterization. Fragmentation of nitroalkanes occurred mainly through loss of the NO(2)(-) anion or neutral loss of HNO(2). The CID of nitroalkenes proceeds via a more complex cyclization, followed by fragmentation to nitrile and aldehyde products. Gas-phase fragmentation of nitroalkene functional groups with additional ? or ? unsaturation occurred through a multiple step cyclization reaction process, leading to 5 and 6 member ring heterocyclic products and carbon chain fragmentation. Cyclization products were not obtained during nitroalkane fragmentation, highlighting the role of double bond ? electrons during NO(2)(-) rearrangements, stabilization and heterocycle formation. The proposed structures, mechanisms and products of fragmentation are supported by analysis of (13)C and (15)N labeled parent molecules, 6 different nitroalkene positional isomers, 6 nitroalkane positional isomers, accurate mass determinations at high resolution and quantum mechanics calculations. Multiple key diagnostic ion fragments were obtained through this analysis, allowing for the precise placement of double bonds and sites of fatty acid nitration, thus supporting an ability to predict nitro positions in biological samples. PMID:21953257

Bonacci, Gustavo; Asciutto, Eliana K; Woodcock, Steven R; Salvatore, Sonia R; Freeman, Bruce A; Schopfer, Francisco J

2011-09-01

238

Engine exhaust particulate and gas phase contributions to vascular toxicity.  

PubMed

Cardiovascular health effects of near-roadway pollution appear more substantial than other sources of air pollution. The underlying cause of this phenomenon may simply be concentration-related, but the possibility remains that gases and particulate matter (PM) may physically interact and further enhance systemic vascular toxicity. To test this, we utilized a common hypercholesterolemic mouse model (Apolipoprotein E-null) exposed to mixed vehicle emission (MVE; combined gasoline and diesel exhausts) for 6?h/d?×?50?d, with additional permutations of removing PM by filtration and also removing gaseous species from PM by denudation. Several vascular bioassays, including matrix metalloproteinase-9 protein, 3-nitrotyrosine and plasma-induced vasodilatory impairments, highlighted that the whole emissions, containing both particulate and gaseous components, was collectively more potent than MVE-derived PM or gas mixtures, alone. Thus, we conclude that inhalation of fresh whole emissions induce greater systemic vascular toxicity than either the particulate or gas phase alone. These findings lend credence to the hypothesis that the near-roadway environment may have a more focused public health impact due to gas-particle interactions. PMID:24730681

Campen, Matthew; Robertson, Sarah; Lund, Amie; Lucero, Joann; McDonald, Jacob

2014-05-01

239

Photoinduced Processes in Cobalt-Complexes: Condensed Phase and Gas Phase  

NASA Astrophysics Data System (ADS)

Femtosecond time-resolved, steady-state spectroscopic methods and quantum chemical calculations are employed to study ultrafast photoinduced processes in [Co(III)-(L-N4Me2)(dbc)](BPh4) and [Co(II)-(L-N4tBu2)(dbsq)](B(p-C6H4Cl)4) and to characterise the transient redox- and spin-states in condensed and gas phase.

Rupp, F.; Chevalier, K.; Wolf, M. M. N.; Krüger, H.-J.; Wüllen, C. v.; Nosenko, Y.; Niedner-Schatteburg, Y.; Riehn, C.; Diller, R.

2013-03-01

240

Diamond nucleation using polyethene  

DOEpatents

The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

Morell, Gerardo; Makarov, Vladimir; Varshney, Deepak; Weiner, Brad

2013-07-23

241

Diamond Nucleation Using Polyethene  

NASA Technical Reports Server (NTRS)

The invention presents a simple, non-destructive and non-abrasive method of diamond nucleation using polyethene. It particularly describes the nucleation of diamond on an electrically viable substrate surface using polyethene via chemical vapor deposition (CVD) technique in a gaseous environment.

Morell, Gerardo (Inventor); Makarov, Vladimir (Inventor); Varshney, Deepak (Inventor); Weiner, Brad (Inventor)

2013-01-01

242

Surfactants from the gas phase may promote cloud droplet formation.  

PubMed

Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8-10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas-aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere. PMID:23382211

Sareen, Neha; Schwier, Allison N; Lathem, Terry L; Nenes, Athanasios; McNeill, V Faye

2013-02-19

243

Surfactants from the gas phase may promote cloud droplet formation  

PubMed Central

Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8–10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas–aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere. PMID:23382211

Sareen, Neha; Schwier, Allison N.; Lathem, Terry L.; Nenes, Athanasios; McNeill, V. Faye

2013-01-01

244

Gas-Phase Dissociation Pathways of Multiply Charged Peptide Clusters  

PubMed Central

Numerous studies of cluster formation and dissociation have been conducted to determine properties of matter in the transition from the condensed phase to the gas phase using materials as diverse as atomic nuclei, noble gasses, metal clusters, and amino acids. Here, electrospray ionization is used to extend the study of cluster dissociation to peptides including leucine enkephalin with 7–19 monomer units and 2–5 protons, and somatostatin with 5 monomer units and 4 protons under conditions where its intramolecular disulfide bond is either oxidized or reduced. Evaporation of neutral monomers and charge separation by cluster fission are the competing dissociation pathways of both peptides. The dominant fission product for all leucine enkephalin clusters studied is a proton-bound dimer, presumably due to the high gas-phase stability of this species. The branching ratio of the fission and evaporation processes for leucine enkephalin clusters appears to be determined by the value of z2/n for the cluster where z is the charge and n the number of monomer units in the cluster. Clusters with low and high values of z2/n dissociate primarily by evaporation and cluster fission respectively, with a sharp transition between dissociation primarily by evaporation and primarily by fission measured at a z2/n value of ~0.5. The dependence of the dissociation pathway of a cluster on z2/n is similar to the dissociation of atomic nuclei and multiply charged metal clusters indicating that leucine enkephalin peptide clusters exist in a state that is more disordered, and possibly fluid, rather than highly structured in the dissociative transition state. The branching ratio, but not the dissociation pathway of [somatostatin5 + 4H]4+ is altered by the reduction of its internal disulfide bond indicating that monomer conformational flexibility plays a role in peptide cluster dissociation. PMID:14652186

Jurchen, John C.; Garcia, David E.; Williams, Evan R.

2005-01-01

245

Musculoskeletal-induced Nucleation in Altitude Decompression Sickness  

NASA Technical Reports Server (NTRS)

Musculoskeletal activity has the potential to both improve and compromise decompression safety. Exercise enhances inert gas elimination during oxygen breathing prior to decompression (prebreathe), but it may also promote bubble nuclei formation (nucleation), which can lead to gas phase separation and bubble growth and increase the risk of decompression sickness (DCS). The timing, pattern and intensity of musculoskeletal activity and the level of tissue supersaturation may be critical to the net effect. There are limited data available to evaluate cost-benefit relationships. Understanding the relationship is important to improve our understanding of the underlying mechanisms of nucleation in exercise prebreathe protocols and to quantify risk in gravity and microgravity environments. Data gathered during NASA's Prebreathe Reduction Program (PRP) studies combined oxygen prebreathe and exercise followed by low pressure (4.3 psi; altitude equivalent of 30,300 ft [9,235 m]) microgravity simulation to produce two protocols used by astronauts preparing for extravehicular activity. Both the Phase II/CEVIS (cycle ergometer vibration isolation system) and ISLE (in-suit light exercise) trials eliminated ambulation to more closely simulate the microgravity environment. The CEVIS results (35 male, 10 female) serve as control data for this NASA/Duke study to investigate the influence of ambulation exercise on bubble formation and the subsequent risk of DCS.

Pollock, N. W.; Natoli, M. J.; Conkin, J.; Wessel, J. H., III; Gernhardt, M. L.

2014-01-01

246

Spectroscopic studies of molecular iodine emitted into the gas phase by seaweed  

NASA Astrophysics Data System (ADS)

Time profiles of molecular iodine emissions from seven species of seaweed have been measured at high time resolution (7.5 s) by direct spectroscopic quantification of the gas phase I2 using broadband cavity enhanced absorption spectroscopy. Substantial differences were found between species, both in the amounts of I2 emitted when the plants were exposed to air and in the shapes of their emission time profiles. Two species of kelp, Laminaria digitata and Laminaria hyperborea, were found to be the most potent emitters, producing an intense burst of I2 when first exposed to air. I2 was also observed from Saccharina latissima and Ascophyllum nodosum but in lower amounts and with broader time profiles. I2 mixing ratios from two Fucus species and Dictyopteris membranacea were at or below the detection limit of the present instrument (25 pptv). A further set of experiments investigated the time dependence of I2 emissions and aerosol particle formation when fragments of L. digitata were exposed to desiccation in air, to ozone and to oligoguluronate stress factors. Particle formation occurred in all L. digitata stress experiments where ozone and light were present, subject to the I2 mixing ratios being above certain threshold amounts. Moreover, the particle number concentrations closely tracked variations in the I2 mixing ratios, confirming the results of previous studies that the condensable particle-forming gases derive from the photochemical oxidation of the plant's I2 emissions. This work also supports the theory that particle nucleation in the coastal atmosphere occurs in "hot-spot" regions of locally elevated concentrations of condensable gases: the greatest atmospheric concentrations of I2 and hence of condensable iodine oxides are likely to be above plants of the most efficiently emitting kelp species and localised in time to shortly after these seaweeds are uncovered by a receding tide.

Ball, S. M.; Hollingsworth, A. M.; Humbles, J.; Leblanc, C.; Potin, P.; McFiggans, G.

2010-07-01

247

Homogeneous nucleation of predominantly cubic ice confined in nanoporous alumina.  

PubMed

The nucleation mechanism of water can be precisely regulated by confinement within nanoporous alumina. We found a transition from heterogeneous nucleation of hexagonal ice (Ih) to homogeneous nucleation of predominantly cubic ice (Ic) with decreasing pore diameter. These results lead to a phase diagram of water under confinement. It contains a (stable) predominant Ic form, a form known to exist only in the upper atmosphere. Possible applications range from cryopreservation to construction materials like cement. PMID:25686014

Suzuki, Yasuhito; Duran, Hatice; Steinhart, Martin; Kappl, Michael; Butt, Hans-Jürgen; Floudas, George

2015-03-11

248

AEROSOL NUCLEATION AND GROWTH DURING LAMINAR TUBE FLOW: MAXIMUM SATURATIONS AND NUCLEATION RATES. (R827354C008)  

EPA Science Inventory

An approximate method of estimating the maximum saturation, the nucleation rate, and the total number nucleated per second during the laminar flow of a hot vapour–gas mixture along a tube with cold walls is described. The basis of the approach is that the temperature an...

249

Conformational Study of Taurine in the Gas Phase  

NASA Astrophysics Data System (ADS)

The conformational preferences of the amino sulfonic acid taurine (NH2-CH2-CH2-SO3H) have been investigated in the gas phase by laser ablation molecular beam Fourier transform microwave spectroscopy (LA-MB-FTMW) in the 6-14 GHz frequency range. One conformer has been observed, and its rotational, centrifugal distortion, and hyperfine quadrupole coupling constants have been determined from the analysis of its rotational spectrum. Comparison of the experimental constants with those calculated theoretically identifies the detected conformer unambiguously. The observed conformer of taurine is stabilized by an intramolecular hydrogen bond O-H···N between the hydrogen of the sulfonic acid group and the nitrogen atom of the amino group.

Cortijo, Vanessa; Sanz, M. Eugenia; López, Juan C.; Alonso, José L.

2009-08-01

250

Gas-phase synthesis of magnetic metal/polymer nanocomposites  

NASA Astrophysics Data System (ADS)

Highly magnetic metal Co nanoparticles were produced via reducing flame spray pyrolysis, and directly coated with an epoxy polymer in flight. The polymer content in the samples varied between 14 and 56 wt% of nominal content. A homogenous dispersion of Co nanoparticles in the resulting nanocomposites was visualized by electron microscopy. The size and crystallinity of the metallic fillers was not affected by the polymer, as shown by XRD and magnetic hysteresis measurements. The good control of the polymer content in the product nanocomposite was shown by elemental analysis. Further, the successful polymerization in the gas phase was demonstrated by electron microscopy and size measurements. The presented effective, dry and scalable one-step synthesis method for highly magnetic metal nanoparticle/polymer composites presented here may drastically decrease production costs and increase industrial yields.

Starsich, Fabian H. L.; Hirt, Ann M.; Stark, Wendelin J.; Grass, Robert N.

2014-12-01

251

Silicon Nanowire-Based Devices for Gas-Phase Sensing  

PubMed Central

Since their introduction in 2001, SiNW-based sensor devices have attracted considerable interest as a general platform for ultra-sensitive, electrical detection of biological and chemical species. Most studies focus on detecting, sensing and monitoring analytes in aqueous solution, but the number of studies on sensing gases and vapors using SiNW-based devices is increasing. This review gives an overview of selected research papers related to the application of electrical SiNW-based devices in the gas phase that have been reported over the past 10 years. Special attention is given to surface modification strategies and the sensing principles involved. In addition, future steps and technological challenges in this field are addressed. PMID:24368699

Cao, Anping; Sudhölter, Ernst J.R.; de Smet, Louis C.P.M.

2014-01-01

252

Reactivity of ambident anions in the gas phase  

NASA Astrophysics Data System (ADS)

Ambident anions are negative ions in which several reactive centra are coupled via resonance. When these ions react, there is a competition possible between the reaction channels via each of these reactive centra. A systematic study on the reactivity of several ambident anions in a Fourier transform ion cyclotron resonance mass spectrometer is described in the thesis. Via probe reactions it is shown that a gas-phase ion/molecule reaction between an ambident anion and an unsaturated polyfluorocarbon compound enables a distinction between the competing reaction channels mentioned. The obtained product distributions can be interpreted using simple perturbation theory. In chapter one of the thesis several models and concepts (such as hard and soft acids and bases, HSAB, perturbation theory and the Allopolarisierungs-Prinzip) are described which have been used previously to explain the reactivity of ambident ions in solution.

Freriks, Ivo. L.

1992-12-01

253

Synthesis and Gas Phase Thermochemistry of Germanium-Containing Compounds  

SciTech Connect

The driving force behind much of the work in this dissertation was to gain further understanding of the unique olefin to carbene isomerization observed in the thermolysis of 1,1-dimethyl-2-methylenesilacyclobutane by finding new examples of it in other silicon and germanium compounds. This lead to the examination of a novel phenylmethylenesilacyclobut-2-ene, which did not undergo olefin to carbene rearrangement. A synthetic route to methylenegermacyclobutanes was developed, but the methylenegermacyclobutane system exhibited kinetic instability, making the study of the system difficult. In any case the germanium system decomposed through a complex mechanism which may not include olefin to carbene isomerization. However, this work lead to the study of the gas phase thermochemistry of a series of dialkylgermylene precursors in order to better understand the mechanism of the thermal decomposition of dialkylgermylenes. The resulting dialkylgermylenes were found to undergo a reversible intramolecular {beta} C-H insertion mechanism.

Nathan Robert Classen

2002-12-31

254

Regenerable Air Purification System for Gas-Phase Contaminant Control  

NASA Technical Reports Server (NTRS)

Tests of a pre-prototype regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an adsorbent column have been performed at NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. During the normal operation mode, contaminants are removed from the air on the column. Regeneration of the column is performed on-line. During regeneration, contaminants are displaced and destroyed inside the closed oxidation loop. In this presentation we discuss initial experimental results for the performance of RAPS in the removal and treatment of several important spacecraft contaminant species from air.

Constantinescu, Ileana C.; Finn, John E.; LeVan, M. Douglas; Lung, Bernadette (Technical Monitor)

2000-01-01

255

Optical properties of anthocyanins in the gas phase  

NASA Astrophysics Data System (ADS)

The gas-phase optical properties of the six most common anthocyanins are studied using time-dependent density-functional theory. Different anthocyanins are classified into three groups, according to the number of low-frequency peaks displayed in the UV-vis spectrum. This behavior is analyzed in terms of one-electron transitions and interaction effects, the latter being rationalized using a suitable double-pole model. Moving from PBE to hybrid exchange-correlation functionals results in a hypsochromic shift of the optical gap. While the colors thus predicted do not quite match those observed in solution, thus highlighting the importance of solvation effects, adoption of hybrid functionals remarkably determines a greater chromatic uniformity of different molecules, in qualitative agreement with experimental evidence in acidic solutions.

Ge, Xiaochuan; Calzolari, Arrigo; Baroni, Stefano

2015-01-01

256

Regenerable Air Purification System for Gas-Phase Contaminant Control  

NASA Technical Reports Server (NTRS)

A regenerable air purification system (RAPS) that uses water vapor to displace adsorbed contaminants from an. adsorbent column into a closed oxidation loop is under development through cooperative R&D between Vanderbilt University and NASA Ames Research Center. A unit based on this design can be used for removing trace gas-phase contaminants from spacecraft cabin air or from polluted process streams including incinerator exhaust. Recent work has focused on fabrication and operation of a RAPS breadboard at NASA Ames, and on measurement of adsorption isotherm data for several important organic compounds at Vanderbilt. These activities support the use and validation of RAPS modeling software also under development at Vanderbilt, which will in turn be used to construct a prototype system later in the project.

Constantinescu, Ileana C.; Qi, Nan; LeVan, M. Douglas; Finn, Cory K.; Finn, John E.; Luna, Bernadette (Technical Monitor)

2000-01-01

257

Gas-Phase Production of Titanium Nitride and Carbide Powders  

NASA Astrophysics Data System (ADS)

The Bureau of Mines investigated a procedure to produce fine-sized titanium nitride, carbide, and carbonitride powders. These powders, because of their high hardness and abrasion resistance, can be substituted for tungsten carbide in some cutting tool applications. Titanium nitride and carbide powders can be cemented together with nickel. The investigated approach produces titanium nitride by reducing titanium tetrachloride with magnesium or sodium vapor in a nitrogen atmosphere at temperatures between 750 and 1,050°C (1,382 and 1,922°F). Titanium carbide and titanium carbonitride can be formed by adding methane to the nitrogen atmosphere. Titanium tetrachloride reduction efficiencies as high as 98% are achieved. X-ray diffraction analyses showed that the powders contain no major impurities. Because the reactions occur in the gas phase, powders finer than 1 ?m are produced.

Harbuck, Donna D.; Davidson, Charles F.; Shirts, Monte B.

1986-09-01

258

Tautomeric properties and gas-phase structure of acetylacetone.  

PubMed

The tautomeric and structural properties of acetylacetone, CH3C(O)CH2C(O)CH3, have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation with different basis sets up to aug-cc-pVTZ). The analysis of GED intensities resulted in the presence of 100(3)% of the enol tautomer at 300(5) K and 64(5)% of the enol at 671(7) K. The enol tautomer possesses Cs symmetry with a planar ring and strongly asymmetric hydrogen bond. The diketo form possesses C2 symmetry. The experimental geometric parameters of both tautomeric forms are reproduced very closely by B3LYP/aug-cc-pVTZ and MP2/cc-pVTZ methods. PMID:24758690

Belova, Natalya V; Oberhammer, Heinz; Trang, Nguen Hoang; Girichev, Georgiy V

2014-06-20

259

Ice nucleation terminology  

NASA Astrophysics Data System (ADS)

Progress in the understanding of ice nucleation is being hampered by the lack of uniformity in how some terms are used in the literature. This even extends to some ambiguity of meanings attached to some terms. Suggestions are put forward here for common use of terms. Some are already well established and clear of ambiguities. Others are less engrained and will need a conscious effort in adoption. Evolution in the range of systems where ice nucleation is being studied enhances the need for a clear nomenclature. The ultimate limit in the clarity of definitions is, of course, the limited degree to which ice nucleation processes are understood.

Vali, G.; DeMott, P.; Möhler, O.; Whale, T. F.

2014-08-01

260

Thermochemical determinations and gas-phase transacetalization reactions studied by tandem mass spectrometry  

Microsoft Academic Search

By using the kinetic method, the proton affinity, gas-phase basicity and gas-phase acidity of urea are determined to be 873.5 ± 5.0, 841.6 ± 5.0, and 1513.8 ± 12.0 kJ\\/mol, respectively. Both the gas-phase basicity and acidity of urea are predominantly controlled by resonance stabilization effects in the corresponding protonated and deprotonated amide moieties. ^ The kinetic method is also

Feng Wang

1999-01-01

261

Gas phase photolysis of pinonaldehyde in the presence of sunlight  

NASA Astrophysics Data System (ADS)

The photolysis of pinonaldehyde in the presence of sunlight and in the presence/absence of an OH radical scavenger (cyclohexane) was studied in a large outdoor smog chamber. More than nine reaction products were identified or tentatively identified and quantified in this study using gas chromatography-mass spectrometry. Carbon yields for pinonaldehyde photolysis in the absence of an OH scavenger are: norpinonaldehyde (21.7%); pinonic acid (11.2%); 3-acetyl-2,2-dimethyl-cyclobutyl-methanol (5.3%); 2,2,3-trimethyl-cyclobutylethanone (2.9%); and 10-oxonorpinonaldehyde (1.9%). Carbon yields for pinonaldehyde photolysis in the presence of cyclohexane are: norpinonaldehyde (20.1%); pinonic acid (0.4%); 3-acetyl-2,2-dimethyl-cyclobutyl-methanol (2.7%); 2,2,3-trimethyl-cyclobutyl-ethanone (1.3%); and 10-oxonorpinonaldehyde (1.0%). The uncertainty in the yield data is estimated to be ˜26%. The results show that pinonaldehyde photolysis is an important part of its overall atmospheric chemistry. A detailed mechanism for pinonaldehyde photolysis in the presence/absence of cyclohexane is proposed, and a kinetic mechanism was used to simulate the gas phase reactions of pinonaldehyde. Observed temporal profiles of pinonaldehyde and its photooxidation products were used to estimate photolysis quantum yields for pinonaldehyde. The atmospheric implications of the data are discussed.

Jaoui, M.; Kamens, R. M.

262

Gas phase hydrogen permeation in alpha titanium and carbon steels  

NASA Technical Reports Server (NTRS)

Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer.

Johnson, D. L.; Shah, K. K.; Reeves, B. H.; Gadgeel, V. L.

1980-01-01

263

Estimation of gas phase mixing in packed beds  

SciTech Connect

An improved model is presented for estimation of the mixing of gaseous species in a packed bed for fuel conversion. In particular, this work clarifies the main characteristics of mixing of volatiles and oxidizers in a burning bed of high-volatile solid fuel. Expressions are introduced to represent the active role of degradation of the solid particles in the mixing within the gas phase. During drying and devolatilization the solids modify the behavior of the gas flow: the volatiles released from the surface of the particles increase the turbulence in the system, and hence the rates of the homogeneous reactions under mixing-limited conditions. Numerical experiments are carried out to test the validity of this conclusion regarding mixing in different geometries. The flow of volatiles leaving the fuel particles is shown to contribute significantly to mixing, especially at low air flows through a bed. However, the fraction of the particle surface where volatiles are released and its orientation in the bed should be better determined in order to increase the accuracy of the estimates of turbulent mixing. (author)

Frigerio, S. [CMIC Dipartimento di Chimica, Materiali e Ingegneria Chimica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan (Italy); Thunman, H.; Leckner, B.; Hermansson, S. [Department of Energy Conversion, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)

2008-04-15

264

Misfit dislocation nucleation in heteroepitaxy  

NASA Astrophysics Data System (ADS)

We have studied atomic mechanisms of misfit dislocation nucleation in heteroepitaxy with semiempirical potentials. Many-body mechanisms of stress relaxation are systematically investigated with Lennard-Jones potential in 2D and 3D cases. Energy barriers for dislocation nucleation are estimated using modern methods for saddle point search (Nudged Elastic Band [1], Eigenvector Following [2] and others). Moreover, new simple and effective method for transition paths searching is proposed. Based on the data the critical thickness of film is estimated as a function of film-substrate lattice misfit. Moreover, to make the study more realistic we used EAM [3] potentials in simulations of Pd/Cu and Cu/Pd systems. We show that the dislocations nucleate more easily in compressive than tensile strained films, and in fcc(111) orientation rather than in fcc(100). These findings are in agreement with recent experimental and theoretical works. 1. H. Jonsson, G. Mills and K. W. Jacobsen, in Classical and Quantum Dynamics in Condensed Phase Simulations, ed. by B. J. Berne, G. Ciccotti, and D. F. Coker (World Scientific, Singapore, 1998). 2. L. J. Munro and D. J. Wales, Phys. Rev. B v59, 3969 (1999), and references therein. 3. S. M. Foiles, M. I. Baskes, and M. S. Daw, Phys. Rev. B v33, 7983 (1986).

Trushin, Oleg; Ying, See Chen; Granato, Enzo; Ala-Nissila, Tapio

2001-03-01

265

Cluster Phase Chemistry: Gas-Phase Reactions of Anionic Sodium Salts of Dicarboxylic Acid Clusters with Water Molecules  

E-print Network

Cluster Phase Chemistry: Gas-Phase Reactions of Anionic Sodium Salts of Dicarboxylic Acid Clusters energy of the cluster correlate well with the cluster phase reactions of oxalate and malonate clusters component of sea salt particles in the atmosphere,12,13 forming sodium dicarboxylic acid clusters. Previous

Goddard III, William A.

266

Gas phase processing of nanostructured titania particles and films: Environmentally benign methodologies  

NASA Astrophysics Data System (ADS)

This dissertation is a study of the gas phase synthesis using flame aerosol reactors to produce nanostructured particles and films with desired features as size, morphology, agglomeration state, crystalline phase composition and modified solid state properties. The following particles/films were produced: titania, lead titanate, Mn-Zn ferrite, Fesp{3+} doped titania and nanocomposites of FeO/TiO. On supercooling titania droplets in flames, metastable anatase was preferentially nucleated. At high flame temperatures of 1570sp°C, 100% anatase spherical titania particles were obtained; at 900 ˜ 1430sp°C, polyhedral shaped particles with mixtures of anatase and rutile were obtained; and at 400sp°C, amorphous titania was obtained. A 3-D computer simulation was used to study the aggregration and restructuring of small clusters in flames. These small aggregates are fractal-like and comply with the fractal power law only in a statistical sense, with a decrease in fractal dimension as the clusters become smaller. A cluster-restructuring model was developed to simulate the topological evolution in a high temperature sintering process. The fractal dimension was found to increase as sintering proceeded for small clusters, in contrast to large clusters where the fractal dimension remained constant. A light scattering technique was used to capture the sintering restructuring of nanosized titania particles in flames by in situ determination of the fractal dimension change of titania agglomerates. Laser Induced Fluorescence was used to optimize flame conditions to produce perovskite structured lead titanate particles in flame reactors. Also, the flame reaction provides a novel method to synthesize Fe(III) doped titania. As the doping concentrations varied from trace to comparable to TiOsb2, solid state properties of titania were modified. Substitutionally doped ferric ion accelerated the anatase-rutile transformation in flames, resulting in a more compact lattice structure and generating oxygen deficiency defects, as revealed by the increased shifting and broadening of anatase peaks in the Raman spectra. Further the UV/VIS absorption spectra was observed to be shifted towards the visible. As the iron dopant increased to the amount of comparable with titanium, the as produced pseudo binary mixture of FeO/TiO had superparamagnetic characteristics indicated by Mossbauer and magnetization measurements. Flame assisted aerosol coating processes were used to deposited titania films onto stainless steel and silica substrates. Deposition mechanisms were studied and related to the film characteristics. Interesting solid state properties were observed as the film thickness diminished to nanoscales. The titania films were tested to have a good anti-corrosive characteristics and other exciting functionality having wide applications.

Yang, Guixiang

267

Energetics of Selected Gas Phase Ion-Molecule Reactions  

NASA Astrophysics Data System (ADS)

The energetics of the gas phase negative ion-molecule association reactions M + X^{-} = McdotX^ {-}, where M are substituted benzenes, quinones and ethylenes and X^{-} are the halide ions (F^{-} , Cl^{-}, Br ^{-} and I^{ -}), were determined by equilibrium measurements with the pulsed electron high pressure mass spectrometer (PHPMS). Evaluation of the equilibrium constants for the halide association (XA) reactions leads directly to absolute bond free energy determinations, -DeltaG _sp{XA}{circ}, in McdotX^{- }. Under conditions where halide association equilibria could not be measured directly, relative bond free energies, -DeltaDeltaG _sp{XA}{circ}, were obtained by measurements of the transfer equilibria McdotX^{-} + M^' = M + cdotM^'cdot X^{-}. Combining -DeltaDeltaG_sp {XA}{circ} values with directly determined -DeltaG _sp{XA}{circ} values leads to further absolute bond free energy determinations. The hydrogen bond free energies in the singly substituted phenol complexes YPhOHcdotBr ^{-}, combined with previous data for X^{-} = Cl ^{-} and I^{ -} from this laboratory, are used to examine the substituent effects on hydrogen bonding. The dominant contribution to YPhOHcdotBr ^{-} stabilization, where the extent of proton transfer from YPhOH to Br^{ -} is small, is due to the field effects of the substituents with pi delocalization playing only a small part. Thus, the correlation with the acidity of YPhOH, where pi delocalization is important, is not very close. Substituent effect analysis of experimentally determined bond free energies and quantum mechanical calculations are used to gain structural information on the complexes McdotX^{-} where M does not possess substituents with protic hydrogens. The results indicate the complexes M cdotX^{-} have a variety of structures, depending on X^ {-} and the nature of the substituents. The temperature dependence of the equilibrium constants for the gas phase reactions HO^ - + HOH = HO^-cdotHOH and CH_3O^- + HOCH_3 = CH_3O ^-cdotHOCH_3 was measured with the PHPMS. The enthalpy and entropy changes were obtained from van't Hoff plots of the equilibrium constants. The enthalpy changes were found to be in good agreement with experimentally determined values reported by Meot-Ner and Sieck and recent theoretical results. The agreement for the entropy changes is found not to be as good. The electron affinities of 20 cyclic diones, mostly substituted maleic and phthalic anhydrides and maleimides and phthalimides, were determined with the PHPMS by measuring gas phase electron transfer equilibria A^ {-} + B = A + B^{ -} involving these compounds and reference compounds whose electron affinities were determined previously. The effects of substituents on electron affinities are similar to those observed previously for other groups of organic compounds.

Paul, Gary John Charles

1990-01-01

268

Measurement of Gas-phase Acids in Diesel Exhaust  

NASA Astrophysics Data System (ADS)

Gas-phase acids were measured using chemical ionization mass spectrometry (CIMS) as part of the Diesel Engine Emission Research Experiment (DEERE). The CIMS technique, utilizing acetate ion (CH3COO-) as a reagent ion, proved to be a rapid (measurements on the order of seconds) and sensitive (several counts/pptv) method of quantifying the acid emissions. Diluted diesel exhaust measurements were made from a Constant Volume Sampling dilution tunnel using a light duty (1.9L turbocharged Volkswagen Jetta TDI) diesel engine equipped with an OEM diesel oxidation catalyst and exhaust gas recirculation, mounted on an engine dynamometer. Acids measured included isocyanic, nitrous, nitric, propionic and sum of lactic and oxalic, as well as other unidentified compounds. Complimentary measurements of CO, CO2, Total Hydrocarbon (THC), and NOx, were also performed. Several engine modes (different engine rpm and torque outputs) at steady state were examined to determine their effect on acid emissions. Emission rates with respect to NOx and fuel based emission factors were determined. Measurements of HONO fuel emission factors agree well with real-world measurements within a traffic tunnel.1 The first estimate of isocyanic acid emission factors from a diesel engine is reported, and suggests that the emission of this highly toxic compound in diesel exhaust should not be ignored. 1. Kurtenbach, R., Becker, K. H., Gomes, J. A. G., Kleffmann, J.,Lorzer, J. C., Spittler, M., Wiesen, P., Ackermann, R., Geyer, A.,and Platt, U.: Investigations of emissions and heterogeneous formation of HONO in a road traffic tunnel, Atmos. Environ., 35, 3385-3394, doi:10.1016/S1352-2310(01)00138-8, 2001.

Wentzell, J. J.; Liggio, J.; Li, S.; Vlasenko, A. L.; Staebler, R. M.; Brook, J.; Lu, G.; Poitras, M.; Chan, T.

2012-12-01

269

Vapor liquid solid-hydride vapor phase epitaxy (VLS-HVPE) growth of ultra-long defect-free GaAs nanowires: Ab initio simulations supporting center nucleation  

SciTech Connect

High aspect ratio, rod-like and single crystal phase GaAs nanowires (NWs) were grown by gold catalyst-assisted hydride vapor phase epitaxy (HVPE). High resolution transmission electron microscopy and micro-Raman spectroscopy revealed polytypism-free zinc blende (ZB) NWs over lengths of several tens of micrometers for a mean diameter of 50 nm. Micro-photoluminescence studies of individual NWs showed linewidths smaller than those reported elsewhere which is consistent with the crystalline quality of the NWs. HVPE makes use of chloride growth precursors GaCl of which high decomposition frequency after adsorption onto the liquid droplet catalysts, favors a direct and rapid introduction of the Ga atoms from the vapor phase into the droplets. High influxes of Ga and As species then yield high axial growth rate of more than 100 ?m/h. The diffusion of the Ga atoms in the liquid droplet towards the interface between the liquid and the solid nanowire was investigated by using density functional theory calculations. The diffusion coefficient of Ga atoms was estimated to be 3 × 10{sup ?9} m{sup 2}/s. The fast diffusion of Ga in the droplet favors nucleation at the liquid-solid line interface at the center of the NW. This is further evidence, provided by an alternative epitaxial method with respect to metal-organic vapor phase epitaxy and molecular beam epitaxy, of the current assumption which states that this type of nucleation should always lead to the formation of the ZB cubic phase.

André, Yamina, E-mail: yamina.andre@univ-bpclermont.fr; Lekhal, Kaddour; Hoggan, Philip; Avit, Geoffrey; Réda Ramdani, M.; Monier, Guillaume; Colas, David; Ajib, Rabih; Castelluci, Dominique; Gil, Evelyne [Clermont Université, Université Blaise Pascal, Institut Pascal, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR6602, Institut Pascal, F-63171 Aubière (France); Cadiz, Fabian; Rowe, Alistair; Paget, Daniel [Physique de la matière condensée, Ecole Polytechnique CNRS, Palaiseau (France); Petit, Elodie [Clermont Université, Université Blaise Pascal, Institut de Chimie de Clermont-Ferrand, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR 6296, ICCF, F-63171 Aubière (France); Leroux, Christine [Université de Toulon, IM2NP, Bât. R, B.P. 20132, 83957 La Garde Cedex (France); CNRS, UMR 7334, 83957 La Garde Cedex (France); Trassoudaine, Agnès [Clermont Université, Université Blaise Pascal, Institut Pascal, BP 10448, F-63000 Clermont-Ferrand (France); CNRS, UMR6602, Institut Pascal, F-63171 Aubière (France); Clermont Université, Université d’Auvergne, BP 10448, F-63000 Clermont-Ferrand (France)

2014-05-21

270

The Gas-Phase Spectra of the 1-INDANYL Radical  

NASA Astrophysics Data System (ADS)

The gas-phase resonant two color two photon ionization (R2C2PI) spectrum of the 1-indanyl radical (m/z=117) has been identified in the region 20800 - 22600 cm^{-1} in a molecular beam. The radical was produced from the discharge of ˜1 % indene in Argon . Laser induced fluorescence (LIF) spectra were recorded in the same region revealing those features observed in R2C2PI. Other precursor molecules were investigated and it was found that the indane precursor resulted in the strongest signal. The fluorescence of the 1-indanyl radical origin band (21158 cm^{-1}) was dispersed in order to determine the ground state vibrational energies. The dispersed fluorescence (DF) spectrum is consistent with the previously observed condensed-phase emission spectrum of the 1-indanyl radical. The DF values were compared with those ground state energies determined by DFT. Franck-Condon factors computed based on the ab initio results showed good agreement with the observed spectrum. Based on the theoretical results we assigned the observed bands. The LIF spectrum contained other bands inconsistent with the 1-indanyl radical. These have been determined to be carried by 1-phenylpropargyl radical and another currently unknown radical determined by R2C2PI to have m/z=133. [1] T. Izumida, K. Inoue, S. Noda, and H. Yoshida, Bull. Chem. Soc. Jpn. 54, 2517 (1981). [2] N. J. Reilly, D. L. Kokkin, M. Nakajima, K. Nauta, S. H. Kable, and T. W. Schmidt, J. Am. Chem. Soc. 130, 3137 (2009).

Troy, Tyler P.; Nakajima, Masakazu; Chalyavi, Nahid; Clady, Raphaël G. C. R.; Nauta, Klaas; Kable, Scott H.; Schmidt, Timothy W.

2009-06-01

271

Volumes of Individual Amino Acid Residues in Gas-Phase Peptide Ions  

E-print Network

Volumes of Individual Amino Acid Residues in Gas-Phase Peptide Ions Anne E. Counterman and David E calculations have been combined to extract average volumes of amino acid residues in gas-phase peptide ions [XxxnLys+H]+ (where Xxx is any amino acid except Lys, Arg, His, and Cys, and n ) 4 to 8). The results

Clemmer, David E.

272

Magnetic resonance velocity imaging of liquid and gas two-phase flow in packed beds  

Microsoft Academic Search

Single-phase liquid flow in porous media such as bead packs and model fixed bed reactors has been well studied by MRI. To some extent this early work represents the necessary preliminary research to address the more challenging problem of two-phase flow of gas and liquid within these systems. In this paper, we present images of both the gas and liquid

M. H. Sankey; D. J. Holland; A. J. Sederman; L. F. Gladden

2009-01-01

273

DEMONSTRATION OF FUEL CELLS TO RECOVER ENERGY FROM LANDFILL GAS: PHASE II. PRETREATMENT SYSTEM PERFORMANCE MEASUREMENT  

EPA Science Inventory

The report describes Phase II of a demonstration of the utilization of commercial phosphoric acid fuel cells to recover energy from landfill gas. This phase consisted primarily of the construction and testing of a Gas Pretreatment Unit (GPU) whose function is to remove those impu...

274

DEMONSTRATION OF FUEL CELLS TO RECOVER ENERGY FROM LANDFILL GAS: PHASE II. PRETREATMENT SYSTEM PERFORMANCE MEASUREMENT  

EPA Science Inventory

The report describes-Phase II of a demonstration of the utilization of commercial phosphoric acid fuel cells to recover energy from landfill gas. his phase consisted primarily of the construction and testing of a Gas Pretreatment Unit (GPU) whose function is to remove those impur...

275

OXYGEN GAS-PHASE ABUNDANCE REVISITED M. K. Andre,1,2  

E-print Network

OXYGEN GAS-PHASE ABUNDANCE REVISITED M. K. Andre´,1,2 C. M. Oliveira,2 J. C. Howk,2 R. Ferlet,1 J gas-phase oxygen abundance along the sight lines toward 19 early-type Galactic stars at an average mag�1 with a standard deviation of 15% is consistent with previous surveys. The mean oxygen abundance

Howk, Jay Christopher

276

DETERMINATION OF GAS-PHASE DIMETHYL SULFATE AND MONOMETHYL HYDROGEN SULFATE  

EPA Science Inventory

Analytical techniques have been developed for the collection and determination of gas phase dimethyl sulfate and monomethyl sulfuric acid in the flue lines and plumes of power plants and in the ambient atmosphere. The techniques involve the collection of the gas phase species in ...

277

Pressure dependent phase stability transformations of GaS: A first principles study  

E-print Network

Pressure dependent phase stability transformations of GaS: A first principles study Bin Wen a principle calculations are used to determine the pressure dependent phase stability transformations for GaS polytypes at pressures up to 1000 GPa. Our results indicate that the relative stability sequence changes

Melnik, Roderick

278

Nuclear symmetry energy effects on liquid-gas phase transition in hot asymmetric nuclear matter  

E-print Network

The liquid-gas phase transition in hot asymmetric nuclear matter is investigated within relativistic mean-field model using the density dependence of nuclear symmetry energy constrained from the measured neutron skin thickness of finite nuclei. We find symmetry energy has a significant influence on several features of liquid-gas phase transition. The boundary and area of the liquid-gas coexistence region, the maximal isospin asymmetry and the critical values of pressure and isospin asymmetry all of which systematically increase with increasing softness in the density dependence of symmetry energy. The critical temperature below which the liquid-gas mixed phase exists is found higher for a softer symmetry energy.

Bharat K. Sharma; Subrata Pal

2010-01-14

279

Importance of the gas phase role to the prediction of energetic material behavior: An experimental study  

NASA Astrophysics Data System (ADS)

Various thermal (radiative, conductive, and convective) initiation experiments are performed to demonstrate the importance of the gas phase role in combustion modeling of energetic materials (EM). A previously published condensed phase model that includes a predicted critical irradiance above which ignition is not possible is compared to experimental laser ignition results for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 2,4,6-trinitrotoluene (TNT). Experimental results conflict with the predicted critical irradiance concept. The failure of the model is believed to result from a misconception about the role of the gas phase in the ignition process of energetic materials. The model assumes that ignition occurs at the surface and that evolution of gases inhibits ignition. High speed video of laser ignition, oven cook-off and hot wire ignition experiments captures the ignition of HMX and TNT in the gas phase. A laser ignition gap test is performed to further evaluate the effect of gas phase laser absorption and gas phase disruption on the ignition process. Results indicate that gas phase absorption of the laser energy is probably not the primary factor governing the gas phase ignition observations. It is discovered that a critical gap between an HMX pellet and a salt window of 6mm±0.4mm exists below which ignition by CO2 laser is not possible at the tested irradiances of 29W /cm2 and 38W/cm2 for HMX ignition. These observations demonstrate that a significant disruption of the gas phase, in certain scenarios, will inhibit ignition, independent of any condensed phase processes. These results underscore the importance of gas phase processes and illustrate that conditions can exist where simple condensed phase models are inadequate to accurately predict the behavior of energetic materials.

Ali, A. N.; Son, S. F.; Asay, B. W.; Sander, R. K.

2005-03-01

280

CHAOS II: Gas-Phase Abundances in NGC 5194  

E-print Network

We have observed NGC5194 (M51a) as part of the CHemical Abundances of Spirals (CHAOS) project. Using the Multi Object Double Spectrographs (MODS) on the Large Binocular Telescope (LBT) we are able to measure one or more of the temperature-sensitive auroral lines ([O III] 4363, [N II] 5755, [S III] 6312) and thus measure "direct" gas-phase abundances in 29 individual HII regions. [O III] 4363 is only detected in two HII regions both of which show indications of excitation by shocks. We compare our data to previous direct abundances measured in NGC5194 and find excellent agreement for all but one region (Delta[log(O/H)] ~ 0.04). We find no evidence of trends in Ar/O, Ne/O, or S/O within NGC5194 or compared to other galaxies. We find modest negative gradients in both O/H and N/O with very little scatter (sigma = -0.62) suggests secondary nitrogen production is responsible for a significantly larger fraction of nitrogen (e.g., factor of 8-10) relative to primary production mechanisms than predicted by theoretica...

Croxall, Kevin V; Berg, Danielle; Skillman, Evan D; Moustakas, John

2015-01-01

281

Gas Phase Dissociation Behavior of Acyl-Arginine Peptides  

PubMed Central

The gas phase dissociation behavior of peptides containing acyl-arginine residues is investigated. These acylations are generated via a combination of ion/ion reactions between arginine-containing peptides and N-hydroxysuccinimide (NHS) esters and subsequent tandem mass spectrometry (MS/MS). Three main dissociation pathways of acylated arginine, labeled Paths 1-3, have been identified and are dependent on the acyl groups. Path 1 involves the acyl-arginine undergoing deguanidination, resulting in the loss of the acyl group and dissociation of the guanidine to generate an ornithine residue. This pathway generates selective cleavage sites based on the recently discussed “ornithine effect”. Path 2 involves the coordinated losses of H2O and NH3 from the acyl-arginine side chain while maintaining the acylation. We propose that Path 2 is initiated via cyclization of the ?-nitrogen of arginine and the C-terminal carbonyl carbon, resulting in rapid rearrangement from the acyl-arginine side chain and the neutral losses. Path 3 occurs when the acyl group contains ?-hydrogens and is observed as a rearrangement to regenerate unmodified arginine while the acylation is lost as a ketene. PMID:24465154

McGee, William M.; McLuckey, Scott A.

2013-01-01

282

Gas phase production and loss of isoprene epoxydiols.  

PubMed

Isoprene epoxydiols (IEPOX) form in high yields from the OH-initiated oxidation of isoprene under low-NO conditions. These compounds contribute significantly to secondary organic aerosol formation. Their gas-phase chemistry has, however, remained largely unexplored. In this study, we characterize the formation of IEPOX isomers from the oxidation of isoprene by OH. We find that cis-?- and trans-?-IEPOX are the dominant isomers produced, and that they are created in an approximate ratio of 1:2 from the low-NO oxidation of isoprene. Three isomers of IEPOX, including cis-?- and trans-?, were synthesized and oxidized by OH in environmental chambers under high- and low-NO conditions. We find that IEPOX reacts with OH at 299 K with rate coefficients of (0.84 ± 0.07) × 10(-11), (1.52 ± 0.07) × 10(-11), and (0.98 ± 0.05) × 10(-11) cm(3) molecule(-1) s(-1) for the ?1, cis-?, and trans-? isomers. Finally, yields of the first-generation products of IEPOX + OH oxidation were measured, and a new mechanism of IEPOX oxidation is proposed here to account for the observed products. The substantial yield of glyoxal and methylglyoxal from IEPOX oxidation may help explain elevated levels of those compounds observed in low-NO environments with high isoprene emissions. PMID:24476509

Bates, Kelvin H; Crounse, John D; St Clair, Jason M; Bennett, Nathan B; Nguyen, Tran B; Seinfeld, John H; Stoltz, Brian M; Wennberg, Paul O

2014-02-20

283

Electron affinities, gas phase acidities, and potential energy curves: Benzene  

NASA Astrophysics Data System (ADS)

The experimental electron affinities of benzene, Ea(Bz), 0.4 to -4.8 eV, are evaluated. Multiple negative ion states are proposed to account for different electron affinities. The semi-empirical procedure known as ?configuration interaction or unrestricted orbitals to relate experimental quantities to self-consistent field values by estimating electron correlation? (CURES-EC) has several advantages: (i) supports multiple Ea(Bz), (ii) supports the Ea(phenyl) and the D(C bond H,Bz), (iii) supports the gas phase acidity of benzene from the latter, (iv) predicts the singlet-triplet split for the phenyl anion of 1.2(2) eV, and (v) predicts the existence of an excited quartet state of the benzene anion with an Ea(Bz), -2.5(2) eV. Nine ionic Morse curves are calculated from CURES-EC properties and experimental data. These are compared with quantum mechanical crossing ?c? potentials obtained using a subroutine in commercial software and ab initio and density functional theory (DFT) procedures. Curves are calculated for the proposed quartet state of the benzene anion.

Jalbout, A. F.; Trzaskowski, B.; Chen, E. C. M.; Chen, E. S.; Adamowicz, Ludwik

284

Wurtzite to Rocksalt Phase Transformation of Cadmium Selenide Nanocrystals via Laser-Induced Shock Waves: Transition from Single to Multiple Nucleation  

NASA Astrophysics Data System (ADS)

The behavior of CdSe nanocrystals shocked to stresses of 2-3.75 GPa has been studied. Above 3 GPa a near-complete disappearance of the first excitonic feature and broadening of the low-energy absorption edge were observed, consistent with a wurtzite to rocksalt structural transformation. The transformation pressure is reduced relative to hydrostatic compression in a diamond anvil cell, and the rate increases, attributed to shock induced shear stress along the reaction coordinate. The especially rapid rate observed for a 3.75 GPa shock suggests multiple nucleation events per particle.

Wittenberg, Joshua S.; Merkle, Maxwell G.; Alivisatos, A. Paul

2009-09-01

285

Wurtzite to rocksalt phase transformation of cadmium selenide nanocrystals via laser-induced shock waves: transition from single to multiple nucleation.  

PubMed

The behavior of CdSe nanocrystals shocked to stresses of 2-3.75 GPa has been studied. Above 3 GPa a near-complete disappearance of the first excitonic feature and broadening of the low-energy absorption edge were observed, consistent with a wurtzite to rocksalt structural transformation. The transformation pressure is reduced relative to hydrostatic compression in a diamond anvil cell, and the rate increases, attributed to shock induced shear stress along the reaction coordinate. The especially rapid rate observed for a 3.75 GPa shock suggests multiple nucleation events per particle. PMID:19792445

Wittenberg, Joshua S; Merkle, Maxwell G; Alivisatos, A Paul

2009-09-18

286

Quantum-Classical Phase Transition of Nucleation Rate in a One-Dimensional Uniaxial Heisenberg Model with a Magnetic Field at an Arbitrary Direction  

NASA Astrophysics Data System (ADS)

We study crossover from quantum tunneling to thermal activation of nucleation rate in a one-dimensional uniaxial Heisenberg model with a magnetic field applied at an arbitrary direction. Considering the periodical boundary condition of spatial coordinate, the type of transition depends critically on the length of ferromagnetic chain. In the low barrier limit two different critical parameter values distinguishing the types of transition are obtained for different angles between the direction of magnetic field and the easy axis (? \\2/ll ?H<< ? and ?H=?).

Zhou, Bin; Liang, Jiu-Qing

287

Heat transfer in gas-liquid and liquid-liquid two phase plug flow systems  

Microsoft Academic Search

Liquid-gas and liquid-liquid two phase flows are examined. It has been recently documented that gas-liquid segmented flows offer a thermal enhancement advantage over single phase flows, since the plug flow (Taylor flow) regime produces internal circulations which enhance radial transport. Additional strategies in liquid-gas and liquid-liquid cooling are being pursued with liquid cooled heat sinks. Proper heat transfer and pressure

N. Janes; Y. S. Muzychka; B. Guy; E. J. Walsh; P. Walsh

2010-01-01

288

Triplet-state energies and substituent effects of excited aroyl compounds in the gas phase.  

PubMed

Triplet-state energy values obtained from the gas phase are still scarce. In this study, the triplet-state energies of 58 aroyl compounds, introduced as gas chromatographic peaks at atmospheric pressure and typically 473 K, have been determined from the 0-0 bands of their n --> pi* type phosphorescence spectra in excited nitrogen. Correlations of those gas-phase triplet-state energies with Hammett constants could be observed for substituted acetophenones, benzaldehydes and benzophenones. PMID:10728860

Lin, Z P; Aue, W A

2000-01-01

289

Photofragmentation of transition-metal-cluster carbonyls in the gas phase  

SciTech Connect

The available data are reviewed for gas-phase photofragmentation of transition-metal-cluster carbonyls. Several new and sophisticated techniques are discussed in relation to the photodissociation of carbonyls, with emphasis on multiphoton-dissociation/ionization methods. The data base obtained for the gas-phase photodissociation of transition-metal clusters is compared to the well-established body of work on cluster compounds in the condensed phase. The new gas-phase results are discussed in light of the predictions coming from electronic-structure theory concerning the photofragmentation of these cluster compounds. 66 references, 6 figures, 2 tables.

Hollingsworth, W.E.; Vaida, V.

1986-03-27

290

Pressure drop, heat transfer, critical heat flux, and flow stability of two-phase flow boiling of water and ethylene glycol/water mixtures - final report for project "Efficent cooling in engines with nucleate boiling."  

SciTech Connect

Because of its order-of-magnitude higher heat transfer rates, there is interest in using controllable two-phase nucleate boiling instead of conventional single-phase forced convection in vehicular cooling systems to remove ever increasing heat loads and to eliminate potential hot spots in engines. However, the fundamental understanding of flow boiling mechanisms of a 50/50 ethylene glycol/water mixture under engineering application conditions is still limited. In addition, it is impractical to precisely maintain the volume concentration ratio of the ethylene glycol/water mixture coolant at 50/50. Therefore, any investigation into engine coolant characteristics should include a range of volume concentration ratios around the nominal 50/50 mark. In this study, the forced convective boiling heat transfer of distilled water and ethylene glycol/water mixtures with volume concentration ratios of 40/60, 50/50, and 60/40 in a 2.98-mm-inner-diameter circular tube has been investigated in both the horizontal flow and the vertical flow. The two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux of the test fluids were determined experimentally over a range of the mass flux, the vapor mass quality, and the inlet subcooling through a new boiling data reduction procedure that allowed the analytical calculation of the fluid boiling temperatures along the experimental test section by applying the ideal mixture assumption and the equilibrium assumption along with Raoult's law. Based on the experimental data, predictive methods for the two-phase pressure drop, the forced convective boiling heat transfer coefficient, and the critical heat flux under engine application conditions were developed. The results summarized in this final project report provide the necessary information for designing and implementing nucleate-boiling vehicular cooling systems.

Yu, W.; France, D. M.; Routbort, J. L. (Energy Systems)

2011-01-19

291

Fragile-to-fragile liquid transition at Tg and stable-glass phase nucleation rate maximum at the Kauzmann temperature TK  

NASA Astrophysics Data System (ADS)

An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change ?p accompanying the enthalpy change -Vm×?p at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at T?Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atom, touching and interpenetrating, are evaluated from nucleation rates. A fragile-to-fragile liquid transition occurs at Tg without stable-glass formation while a strong glass is stable after transition.

Tournier, Robert F.

2014-12-01

292

Fragile-to-fragile Liquid Transition at Tg and Stable-Glass Phase Nucleation Rate Maximum at the Kauzmann Temperature TK  

E-print Network

An undercooled liquid is unstable. The driving force of the glass transition at Tg is a change of the undercooled-liquid Gibbs free energy. The classical Gibbs free energy change for a crystal formation is completed including an enthalpy saving. The crystal growth critical nucleus is used as a probe to observe the Laplace pressure change Dp accompanying the enthalpy change -Vm *Dp at Tg where Vm is the molar volume. A stable glass-liquid transition model predicts the specific heat jump of fragile liquids at temperatures smaller than Tg, the Kauzmann temperature TK where the liquid entropy excess with regard to crystal goes to zero, the equilibrium enthalpy between TK and Tg, the maximum nucleation rate at TK of superclusters containing magic atom numbers, and the equilibrium latent heats at Tg and TK. Strong-to-fragile and strong-to-strong liquid transitions at Tg are also described and all their thermodynamic parameters are determined from their specific heat jumps. The existence of fragile liquids quenched in the amorphous state, which do not undergo liquid-liquid transition during heating preceding their crystallization, is predicted. Long ageing times leading to the formation at TK of a stable glass composed of superclusters containing up to 147 atoms, touching and interpenetrating, are evaluated from nucleation rates. A fragile-to-fragile liquid transition occurs at Tg without stable-glass formation while a strong glass is stable after transition.

Robert Felix Tournier

2015-02-23

293

Properties of Ice Clusters from an Analysis of Freezing Nucleation Ian J. Ford  

E-print Network

Properties of Ice Clusters from an Analysis of Freezing Nucleation Ian J. Ford DepartmentVed: April 18, 2001; In Final Form: August 10, 2001 Properties of the critical clusters that are instrumental in the nucleation of a first-order phase transition can be obtained through the analysis of nucleation rate data

Ford, Ian

294

Gas–liquid two-phase flow distributions in parallel channels for fuel cells  

Microsoft Academic Search

In the present study, gas–liquid two-phase flow in a parallel square minichannel system oriented horizontally and at an incline is studied under operating conditions relevant to fuel cell operations. Flow mal-distribution in parallel channels occurs at low gas and liquid flow rates. In general, high superficial gas velocities are required to ensure even flow distribution, and the minimum gas flow

Lifeng Zhang; Wei Du; Hsiaotao T. Bi; David P. Wilkinson; Jürgen Stumper; Haijiang Wang

2009-01-01

295

Colloids and Nucleation  

NASA Technical Reports Server (NTRS)

The objectives of the work funded under this grant were to develop a microphotographic technique and use it to monitor the nucleation and growth of crystals of hard colloidal spheres. Special attention is given to the possible need for microgravity studies in future experiments. A number of persons have been involved in this work. A masters student, Keith Davis, began the project and developed a sheet illumination apparatus and an image processing system for detection and analysis. His work on a segmentation program for image processing was sufficient for his master's research and has been published. A post doctoral student Bernie Olivier and a graduate student Yueming He, who originally suggested the sheet illumination, were funded by another source but along with Keith made photographic series of several samples (that had been made by Keith Davis). Data extraction has been done by Keith, Bernie, Yueming and two undergraduates employed on the grant. Results are published in Langmuir. These results describe the sheet lighting technique as one which illuminates not only the Bragg scattering crystal, but all the crystals. Thus, accurate crystal counts can be made for nucleation rate measurements. The strange crystal length scale reduction, observed in small angle light scattering (SALS) studies, following the initial nucleation and growth period, has been observed directly. The Bragg scattering (and dark) crystal size decreases in the crossover region. This could be an effect due to gravitational forces or due to over- compression of the crystal during growth. Direct observations indicate a complex morphology for the resulting hard sphere crystals. The crystal edges are fairly sharp but the crystals have a large degree of internal structure. This structure is a result of (unstable) growth and not aggregation. As yet unpublished work compares growth exponents data with data obtained by SALS. The nucleation rate density is determined over a broad volume fraction range (0.505 to 0.575) and compared to classical nucleation rate calculations. The experimental nucleation rate density varies with volume fraction more slowly than expected theoretically. Gravity may influence nucleation because crystal nuclei are more dense than the surrounding fluid and may be gravitationally convected. The largest observed crystal size was near volume fraction 0.52. Near the freezing point, crystals should grow to large size because nuclei are sparse and there is plenty of room to grow without contacting other crystals. Near melting the opposite is true, with crystals growing into one another shortly after nucleation. The maximum crystal size seen near 0.52 volume fraction suggests that gravitational stresses are limiting crystal growth near freezing.

Ackerson, Bruce

1997-01-01

296

Numerical analysis of discrete phase induced effects on a gas flow in a turbulent two-phase free jet  

Microsoft Academic Search

The paper addresses numerical simulation of turbulent two-phase flow in a long vertical tube and turbulent two-phase free jet formed at the tube outlet, analyzing agreement between the numerical results and the results of corresponding experimental investigation carried out earlier.In the numerical analyses conducted, gas phase was modeled as an air flow (having a mass flow-rate in the range of

Milan B. Staki?; Goran S. Živkovi?; Miroslav A. Sijer?i?

2011-01-01

297

Homogeneous crystal nucleation in binary metallic melts  

NASA Technical Reports Server (NTRS)

A method for calculating the homogeneous crystal nucleation frequency in binary metallic melts is developed. The free energy of crystallization is derived from regular solution models for the liquid and solid and is used, together with model-based estimates of the interfacial tension, to calculate the nucleation frequency from the classical theory. The method can account for the composition dependence of the maximum undercooling observed in a number of experiments on small droplet dispersions. It can also be used to calculate the driving force for crystal growth and to obtain more precise estimates of the homogeneous crystal nucleation frequency in glass-forming alloys. This method, although approximate, is simple to apply, and requires only knowledge of the phase diagram and a few readily available thermodynamic quantities as input data.

Thompson, C. V.; Spaepen, F.

1983-01-01

298

Diamond nucleation and growth at the early stages on Si(100) monitored by electron spectroscopies  

NASA Astrophysics Data System (ADS)

Diamond growth on Si(100) is studied by scanning Auger microscopy (SAM), Auger electron spectroscopy (AES), electron loss spectroscopy (ELS) and X-ray photoelectron spectroscopy (XPS) focussing on the early stages of nucleation and growth. The low nucleation density allows us to monitor the evolution of both the substrate and the deposit intensities during the deposition process. Using the structural and chemical imaging probe provided by scanning Auger electron microscopy, we localize areas formed by carbon, only of diamond-type, and featureless areas with C, Si and O. The carbon nature on these last domains is initially a complex mixture of amorphous carbon, carbide and diamond. The amorphous deposit rapidly disappears (30 min), but the occurrence of surface carbide is still detected even after 120 min of growth. The surface carbon content, recorded both by AES focussed on the featureless domains and by XPS, initially drops. This is interpreted by the formation of silicon carbide embedding or removing the amorphous carbon layer. We identify three different sites of nucleation, which are (i) diamond seeds left by the substrate pretreatment; (ii) amorphous carbon at the very beginning of the nucleation process and (iii) silicon carbide. Then the diamond growth and the carbide formation are competitive processes, limited by (i) the reactive content in the gas phase and (ii) diffusion and etching of the silicon.

Le Normand, F.; Ababou, A.; Braul, N.; Carriére, B.; Fayette, L.; Marcus, B.; Mermoux, M.; Romeo, M.; Speisser, C.

1994-11-01

299

Gas-Phase Combustion Synthesis of Aluminum Nitride Powder  

NASA Technical Reports Server (NTRS)

Due to its combined properties of high electrical resistivity and high thermal conductivity aluminum nitride (AlN) is a highly desirable material for electronics applications. Methods are being sought for synthesis of unagglomerated, nanometer-sized powders of this material, prepared in such a way that they can be consolidated into solid compacts having minimal oxygen content. A procedure for synthesizing these powders through gas-phase combustion is described. This novel approach involves reacting AlCl3, NH3, and Na vapors. Equilibrium thermodynamic calculations show that 100% yields can be obtained for these reactants with the products being AlN, NaCl, and H2. The NaCl by-product is used to coat the AlN particles in situ. The coating allows for control of AlN agglomeration and protects the powders from hydrolysis during post-flame handling. On the basis of thermodynamic and kinetic considerations, two different approaches were employed to produce the powder, in co-flow diffusion flame configurations. In the first approach, the three reactants were supplied in separate streams. In the second, the AlCl3 and NH3 were premixed with HCl and then reacted with Na vapor. X-ray diffraction (XRD) spectra of as-produced powders show only NaCl for the first case and NaCl and AlN for the second. After annealing at 775 C tinder dynamic vacuum, the salt was removed and XRD spectra of powders from both approaches show only AlN. Aluminum metal was also produced in the co-flow flame by reacting AlCl3 with Na. XRD spectra of as-produced powders show the products to be only NaCl and elemental aluminum.

Axelbaum, R. L.; Lottes, C. R.; Huertas, J. I.; Rosen, L. J.

1996-01-01

300

Proton irradiation of DNA nucleosides in the gas phase.  

PubMed

The four DNA nucleosides guanosine, adenosine, cytidine and thymidine have been produced in the gas phase by a laser thermal desorption source, and irradiated by a beam of protons with 5 keV kinetic energy. The molecular ions as well as energetic neutrals formed have been analyzed by mass spectrometry in order to shed light on the ionization and fragmentation processes triggered by proton collision. A range of 8-20 eV has been estimated for the binding energy of the electron captured by the proton. Glycosidic bond cleavage between the base and sugar has been observed with a high probability for all nucleosides, resulting in predominantly intact base ions for guanosine, adenosine, and cytidine but not for thymidine where intact sugar ions are dominant. This behavior is influenced by the ionization energies of the nucleobases (G < A < C < T), which seems to determine the localization of the charge following the initial ionization. This charge transfer process can also be inferred from the production of protonated base ions, which have a similar dependence on the base ionization potential, although the base proton affinity might also play a role. Other dissociation pathways have also been identified, including further fragmentation of the base and sugar moieties for thymidine and guanosine, respectively, and partial breakup of the sugar ring without glycosidic bond cleavage mainly for adenosine and cytidine. These results show that charge localization following ionization by proton irradiation is important in determining dissociation channels of isolated nucleosides, which could in turn influence direct radiation damage in DNA. PMID:25691342

Poully, Jean-Christophe; Miles, Jordan; De Camillis, Simone; Cassimi, Amine; Greenwood, Jason B

2015-03-01

301

Gas-Phase Combustion Synthesis of Nonoxide Nanoparticles in Microgravity  

NASA Technical Reports Server (NTRS)

Gas-phase combustion synthesis is a promising process for creating nanoparticles for the growing nanostructure materials industry. The challenges that must be addressed are controlling particle size, preventing hard agglomerates, maintaining purity, and, if nonoxides are synthesized, protecting the particles from oxidation and/or hydrolysis during post-processing. Sodium-halide Flame Encapsulation (SFE) is a unique methodology for producing nonoxide nanoparticles that addresses these challenges. This flame synthesis process incorporates sodium and metal-halide chemistry, resulting in nanoparticles that are encapsulated in salt during the early stages of their growth in the flame. Salt encapsulation has been shown to allow control of particle size and morphology, while serving as an effective protective coating for preserving the purity of the core particles. Metals and compounds that have been produced using this technology include Al, W, Ti, TiB2, AlN, and composites of W-Ti and Al-AlN. Oxygen content in SFE synthesized nano- AlN has been measured by neutron activation analysis to be as low as 0.54wt.%, as compared to over 5wt.% for unprotected AlN of comparable size. The overall objective of this work is to study the SFE process and nano-encapsulation so that they can be used to produce novel and superior materials. SFE experiments in microgravity allow the study of flame and particle dynamics without the influence of buoyancy forces. Spherical sodium-halide flames are produced in microgravity by ejecting the halide from a spherical porous burner into a quiescent atmosphere of sodium vapor and argon. Experiments are performed in the 2.2 sec Drop Tower at the NASA-Glenn Research Center. Numerical models of the flame and particle dynamics were developed and are compared with the experimental results.

Axelbaum, R. L.; Kumfer, B. M.; Sun, Z.; Chao, B. H.

2001-01-01

302

IV-VI semiconductor lasers for gas phase biomarker detection  

NASA Astrophysics Data System (ADS)

A promising absorption spectroscopy application for mid-IR lasers is exhaled breath analysis where sensitive, selective, and speedy measurement of small gas phase biomarker molecules can be used to diagnose disease and monitor therapies. Many molecules such as nitric oxide, ethane, formaldehyde, acetaldehyde, acetone, carbonyl sulfide, and carbon disulfide have been connected to diseases or conditions such as asthma, oxidative stress, breast cancer, lung cancer, diabetes, organ transplant rejection, and schizophrenia. Measuring these and other, yet to be discovered, biomarker molecules in exhaled breath with mid-IR lasers offers great potential for improving health care since such tests are non-invasive, real-time, and do not require expensive consumables or chemical reagents. Motivated by these potential benefits, mid-IR laser spectrometers equipped with presently available cryogenically-cooled IV-VI lasers mounted in compact Stirling coolers have been developed for clinical research applications. This paper will begin with a description of the development of mid-IR laser instruments and their use in the largest known exhaled breath clinical study ever performed. It will then shift to a description of recent work on the development of new IV-VI semiconductor quantum well materials and laser fabrication methods that offer the promise of low power consumption (i.e. efficient) continuous wave emission at room temperature. Taken together, the demonstration of compelling clinical applications with large market opportunities and the clear identification of a viable pathway to develop low cost mid-IR laser instrumentation can create a renewed focus for future research and development efforts within the mid-IR materials and devices area.

McCann, Patrick; Namjou, Khosrow; Roller, Chad; McMillen, Gina; Kamat, Pratyuma

2007-09-01

303

Measurement of soil/dust arsenic by gas phase chemiluminescence.  

PubMed

A gas phase chemiluminescence (GPCL)-based method for trace measurement of arsenic has been recently described for the measurement of arsenic in water. The principle is based on the reduction of inorganic As to AsH(3) at a controlled pH (the choice of pH governs whether only As(III) or all inorganic As is converted) and the reaction of AsH(3) with O(3) to produce chemiluminescence (Idowu et al., Anal. Chem. 78 (2006) 7088-7097). The same general principle has also been used in postcolumn reaction detection of As, where As species are separated chromatographically, then converted into inorganic As by passing through a UV photochemical reactor followed by AsH(3) generation and CL reaction with ozone (Idowu and Dasgupta, Anal. Chem. 79 (2007) 9197-9204). In the present paper we describe the measurement of As in different soil and dust samples by serial extraction with water, citric acid, sulfuric acid and nitric acid. We also compare parallel measurements for total As by induction coupled plasma mass spectrometry (ICP-MS). As(V) was the only species found in our samples. Because of chloride interference of isobaric ArCl(+) ICP-MS analyses could only be carried out by standard addition; these results were highly correlated with direct GPCL and LC-GPCL results (r(2)=0.9935 and 1.0000, respectively). The limit of detection (LOD) in the extracts was 0.36 microg/L by direct GPCL compared to 0.1 microg/L by ICP-MS. In sulfuric acid-based extracts, the LC-GPCL method provided LODs inferior to those previously observed for water-based standards and were 2.6, 1.3, 6.7, and 6.4 microg/L for As(III), As(V), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA), respectively. PMID:18804648

Sawalha, Maather F; Sengupta, Mrinal K; Ohira, Shin-Ichi; Idowu, Ademola D; Gill, Thomas E; Rojo, Lila; Barnes, Melanie; Dasgupta, Purnendu K

2008-10-19

304

Coupled Nucleation Processes in Metallic Liquids and Glasses  

NASA Astrophysics Data System (ADS)

Nucleation processes in condensed systems are often more complicated than expected from classical theory considerations. For example, our recent studies of glasses and deeply supercooled liquids demonstrate that the short- and medium-range order play an important role in the nucleation pathway. High-energy X-ray diffraction data from electrostatically levitated transition metal and alloy liquids demonstrate the frequent development of icosahedral short-range order (ISRO) with supercooling. This ordering has significant consequences for crystallization and vitrification of the liquids. It makes it difficult to nucleate ordered crystal phases, confirming a half-century old hypothesis by Frank. Measurements of the density and surface tension in several supercooled liquids suggest that it may be associated with a liquid/liquid phase transition. Quantitative measurements of the time-dependent nucleation rate in a Zr59Ti3Cu20Ni8Al10 metallic glass and associated structural studies of the supercooled liquid demonstrate that it increases through the glass transition, providing support for a frustration model of the glass transition. In a Ti-Zr-Ni liquid the ISRO lowers the barrier for a metastable icosahedral quasicrystal, blurring the distinction between homogenous and heterogeneous nucleation. Our studies and those of others suggest that the nucleation of the ordered phase can be coupled with liquid phase transitions, including high order transitions. Coupling between other processes is also common for nucleation. For example, the coupling between the stochastic fluxes of interfacial attachment and long-range diffusion in the nucleation step can be critical when the initial and final phases have different chemical compositions. The implications of coupled nucleation processes on phase formation, stability and nanoscale crystallization are discussed.

Kelton, Ken

2009-03-01

305

Molecular Dynamics Simulation of Homogeneous Crystal Nucleation in Polyethylene  

E-print Network

Using a realistic united-atom force field, molecular dynamics simulations were performed to study homogeneous nucleation of the crystal phase at about 30% supercooling from the melts of n-pentacontahectane (C150) and a ...

Yi, Peng

306

Homogeneous nucleation rate measurements in supersaturated water vapor.  

PubMed

The rate of homogeneous nucleation in supersaturated vapors of water was studied experimentally using a thermal diffusion cloud chamber. Helium was used as a carrier gas. Our study covers a range of nucleation rates from 3x10(-1) to 3x10(2) cm(-3) s(-1) at four isotherms: 290, 300, 310, and 320 K. The molecular content of critical clusters was estimated from the slopes of experimental data. The measured isothermal dependencies of nucleation rate of water on saturation ratio were compared with the prediction of the classical theory of homogeneous nucleation, the empirical prediction of Wolk et al. [J. Chem. Phys. 117, 10 (2002)], the scaled model of Hale [Phys. Rev. A 33, 4156 (1986)], and the former nucleation onset data. PMID:19045352

Brus, David; Zdímal, Vladimír; Smolík, Jirí

2008-11-01

307

CO2 Capture from Flue Gas by Phase Transitional Absorption  

SciTech Connect

A novel absorption process called Phase Transitional Absorption was invented. What is the Phase Transitional Absorption? Phase Transitional Absorption is a two or multi phase absorption system, CO{sub 2} rich phase and CO{sub 2} lean phase. During Absorption, CO{sub 2} is accumulated in CO{sub 2} rich phase. After separating the two phases, CO{sub 2} rich phase is forward to regeneration. After regeneration, the regenerated CO{sub 2} rich phase combines CO{sub 2} lean phase to form absorbent again to complete the cycle. The advantage for Phase Transitional Absorption is obvious, significantly saving on regeneration energy. Because CO{sub 2} lean phase was separated before regeneration, only CO{sub 2} rich phase was forward to regeneration. The absorption system we developed has the features of high absorption rate, high loading and working capacity, low corrosion, low regeneration heat, no toxic to environment, etc. The process evaluation shows that our process is able to save 80% energy cost by comparing with MEA process.

Liang Hu

2009-06-30

308

Stages of homogeneous nucleation in solid isotopic helium mixtures.  

PubMed

We have made pressure and NMR measurements during the evolution of phase separation in solid helium isotopic mixtures. Our observations indicate clearly all three stages of the homogeneous nucleation-growth process: (1) creation of nucleation sites; (2) growth of the new-phase component at these nucleation sites; and (3) coarsening: the dissolution of subcritical droplets with the consequent further late-stage growth of the supercritical droplets. The time exponent for the coarsening, a=1/3, is consistent with the conserved order parameter Lifshitz-Slezov evaporation-condensation mechanism. PMID:18352566

Poole, M; Saunders, J; Cowan, B

2008-02-22

309

The gas-phase thermal chemistry of tetralin and related model systems  

SciTech Connect

The thesis is divided into 5 papers: gas-phase thermal decomposition of tetralin; flash vacuum pyrolysis of 3-benzocycloheptenone and 1,3, 4,5-tetrahydro-2-benzothiepin-2,2-dioxide (model systems for gas-phase pyrolysis of tetralin); high-temperature gas-phase reactions of o-allylbenzyl radicals generated by flash vacuum pyrolysis of is(o-allylbenzyl) oxalate; flash vacuum pyrolysis of 1,4-diphenylbutane; and flash vacuum pyrolysis of o-allyltoluene, o-(3-butenyl)toluene and o-(pentenyl)toluene were also used.

Malandra, J.

1993-05-01

310

Gas phase dispersion in compost as a function of different water contents and air flow rates  

NASA Astrophysics Data System (ADS)

Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as a function of gas flow velocity and compost volumetric water content using oxygen and nitrogen as tracer gases. The compost was chosen because it has a very wide water content range and because it represents a wide range of porous media, including soils and biofilter media. Column breakthrough curves for oxygen and nitrogen were measured at relatively low pore gas velocities, corresponding to those observed in for instance soil vapor extraction systems or biofilters for air cleaning at biogas plants or composting facilities. Total gas mechanical dispersion-molecular diffusion coefficients were fitted from the breakthrough curves using a one-dimensional numerical solution to the advection-dispersion equation and used to determine gas dispersivities at different volumetric gas contents. The results showed that gas mechanical dispersion dominated over molecular diffusion with mechanical dispersion for all water contents and pore gas velocities investigated. Importance of mechanical dispersion increased with increasing pore gas velocity and compost water content. The results further showed that gas dispersivity was relatively constant at high values of compost gas-filled porosity but increased with decreasing gas-filled porosity at lower values of gas-filled porosity. Results finally showed that measurement uncertainty in gas dispersivity is generally highest at low values of pore gas velocity.

Sharma, Prabhakar; Poulsen, Tjalfe G.

2009-07-01

311

Direct preparation of dichloropropanol from glycerol and hydrochloric acid gas using heteropolyacid (HPA) catalyst by heterogeneous gas phase reaction  

Microsoft Academic Search

Direct preparation of dichloropropanol (DCP) from glycerol and hydrochloric acid gas was carried out in a heterogeneous gas phase reactor using H3PMo12?XWXO40 (X=0, 3, 6, 9, and 12), H4SiW12O40, and H4SiMo12O40 heteropolyacid (HPA) catalysts. Acid property of the HPA catalyst was determined by NH3-TPD measurement in order to correlate the catalytic activity with the acid property of the catalyst. Acid

Sun Ho Song; Dong Ryul Park; Sung Yul Woo; Won Seob Song; Myong Suk Kwon; In Kyu Song

2010-01-01

312

FLUE GAS DESULFURIZATION PILOT STUDY. PHASE II. APPLICABILITY STUDY  

EPA Science Inventory

The North Atlantic Treaty Organization Committee on the Challenges of Modern Society (NATO-CCMS) Flue Gas Desulfurization (FGD) Study Group prepared status reports on 12 FGD processes. Results of this work are summarized in NATO Report No. 95 titled 'Flue Gas Desulfurization Pilo...

313

Small gas-phase dianions produced by sputtering and gas flooding.  

PubMed

We have extended our previous experiment [Schauer et al., Phys. Rev. Lett. 65, 625 (1990)] where we had produced small gas-phase dianion clusters of C(n) (2-)(n > or =7) by means of sputtering a graphite surface by Cs(+) ion bombardment. Our detection sensitivity for small C(n) (2-) could now be increased by a factor of about 50 for odd n. Nevertheless, a search for the elusive pentamer dianion of C(5) (2-) was not successful. As an upper limit, the sputtered flux of C(5) (2-) must be at least a factor of 5000 lower than that of C(7) (2-), provided that the lifetime of C(5) (2-) is sufficiently long to allow its detection by mass spectrometry. When oxygen gas (flooding with either O(2) or with N(2)O) was supplied to the Cs(+)-bombarded graphite surface, small dianions of OC(n) (2-)(5< or =n < or =14) and O(2)C(7) (2-) were observed in addition to C(n) (2-)(n > or =7). Similarly, Cs(+) sputtering of graphite with simultaneous SF(6) gas flooding produced SC(n) (2-)(6< or =n< or =18). Mixed nitrogen-carbon or fluorine-carbon dianion clusters could not be observed by these means. Attempts to detect mixed metal-fluoride dianions for SF(6) gas flooding of various Cs(+)-bombarded metal surfaces were successful for the case of Zr, where metastable ZrF(6) (2-) was observed. Cs(+) bombardment of a silicon carbide (SiC) wafer produced SiC(n) (2-) (n=6,8,10). When oxygen gas was supplied to the Cs(+)-bombarded SiC surface, small dianions of SiOC(n) (2-) (n=4,6,8) and of SiO(2)C(n) (2-) (n=4,6) as well as a heavier unidentified dianion (at mz=98.5) were observed. For toluene (C(7)H(8)) vapor flooding of a Cs(+)-bombarded graphite surface, several hydrocarbon dianion clusters of C(n)H(m) (2-)(n> or =7) were produced in addition to C(n) (2-)(n> or =7), while smaller C(n)H(m) (2-) with n< or =6 could not be observed. BeC(n) (2-) (n=4,6,8,10), Be(2)C(6) (2-), as well as BeC(8)H(m) (2-) (with m=2 and/or m=1) were observed for toluene vapor flooding of a Cs(+)-bombarded beryllium metal foil. The metastable pentamer (9)Be(12)C(4) (2-) at mz=28.5 was the smallest and lightest dianion molecule that we could detect. The small dianion clusters of SC(n) (2-), OC(n) (2-), BeC(n) (2-), and SiO(m)C(n) (2-) (m=0,1,2) have different abundance patterns. A resemblance exists between the abundance patterns of BeC(n) (2-) and SiC(n) (2-), even though calculated molecular structures of BeC(6) (2-) and SiC(6) (2-) are different. The abundance pattern of SC(n) (2-) is fairly similar to that of C(n) (2-). PMID:16375481

Franzreb, Klaus; Williams, Peter

2005-12-01

314

Nucleation in a Fermi liquid at negative pressure  

E-print Network

Experimental investigation of cavitation in liquid helium 3 has revealed a singular behaviour in the degenerate region at low temperature. As the temperature decreases below 80 mK, the cavitation pressure becomes significantly more negative. To investigate this, we have extrapolated the Fermi parameters in the negative pressure region. This allowed us to calculate the zero sound velocity, which we found to remain finite at the spinodal limit where the first sound velocity vanishes. We discuss the impact on the nucleation of the gas phase in terms of a quantum stiffness of the Fermi liquid. As a result we predict a cavitation pressure which is nearer to the spinodal line than previously thought.

Frederic Caupin; Sebastien Balibar; Humphrey J. Maris

2001-09-19

315

Measurements of cross-sectional instantaneous phase distribution in gas–liquid pipe flow  

Microsoft Academic Search

Two novel complementing methods that enable experimental study of gas and liquid phases distribution in two-phase pipe flow are considered. The first measuring technique uses a wire-mesh sensor that, in addition to providing data on instantaneous phase distribution in the pipe cross-section, also allows measuring instantaneous propagation velocities of the phase interface. A novel algorithm for processing the wire-mesh sensor

E. Roitberg; L. Shemer; D. Barnea

2007-01-01

316

An investigation into the flow behavior of a single phase gas system and a two phase gas/liquid system in normal gravity with nonuniform heating from above  

NASA Technical Reports Server (NTRS)

The fluid behavior in normal gravity of a single phase gas system and a two phase gas/liquid system in an enclosed circular cylinder heated suddenly and nonuniformly from above was investigated. Flow visualization was used to obtain qualitative data on both systems. The use of thermochromatic liquid crystal particles as liquid phase flow tracers was evaluated as a possible means of simultaneously gathering both flow pattern and temperature gradient data for the two phase system. The results of the flow visualization experiments performed on both systems can be used to gain a better understanding of the behavior of such systems in a reduced gravity environment and aid in the verification of a numerical model of the system.

Disimile, Peter J.; Heist, Timothy J.

1990-01-01

317

Investigation of ice nucleation properties of mineral and soil particles  

NASA Astrophysics Data System (ADS)

Number fractions of different types of submicron mineral (kaolinite) and soil (China loess soils and agricultural soils from different crops) particles capable of nucleating ice under mixed-phase cloud conditions were investigated using a continuous flow diffusion ice chamber (CFDC). We found that both China loess and agricultural soil particles are better ice nucleators than kaolinite particles particularly at warmer temperatures. We also found that although the ice nucleation properties of untreated China loess and agricultural soil particles are relatively similar to each other, agricultural soil particles lose their ice nucleating ability after heat treatment at 300°C. Our results suggest that agricultural soils contain rich organic matter, which can play a key role in enhancing their ice nucleating ability.

Tobo, Yutaka; DeMott, Paul J.; Prenni, Anthony J.; Hill, Thomas C.; Franc, Gary D.; Kreidenweis, Sonia M.

2013-05-01

318

Duration of nucleation process in supercooled halide melts  

NASA Astrophysics Data System (ADS)

We present a model allowing to estimate the so-called time lag of nucleating halide melts using electrical conductivity measurements. Due to the complex-forming nature of molten halide salts we suppose two basic types of charge carriers in the melt: complexes (playing the role of monomers—building units) and clusters of a newly forming solid phase. Within context of the nonstationary nucleation theory we determined a formula expressing the time dependency of electrical conductivity of such a system and compared this result with the experimental data obtained for the melts of PbBr2, PbCl2, and KPb2Cl5. In terms of this formula the time lag of nucleation may be estimated. This important quantity characterizing the moment from which the nucleated clusters only grow to the macroscopic sizes has been found to be approximately 75% of the total duration of the nucleation process itself.

Demo, P.; Sveshnikov, A. M.; Nitsch, K.; Rodová, M.; Kožíšek, Z.

2005-08-01

319

Fluorescence resonance energy transfer of gas-phase ions under ultra high vacuum and ambient conditions.  

PubMed

We report evidence for fluorescence resonance energy transfer (FRET) of gas-phase ions under ultra high vacuum conditions (10(-9) mbar) inside a mass spectrometer as well as under ambient conditions inside an electrospray plume. Two different FRET pairs based on carboxyrhodamine 6G (donor) and ATTO590 or Bodipy TR (acceptor) dyes were examined and their gas-phase optical properties were studied. Our measurements indicate a different behavior for the two FRET pairs, which can be attributed to their different conformations in the gas phase. Upon desolvation via electrospray ionization, one of the FRET pairs undergoes a conformational change that leads to disappearance of FRET. This study shows the promise of FRET to obtain a direct correlation between solution and gas-phase structures. PMID:24691138

Frankevich, Vladimir; Chagovets, Vitaliy; Widjaja, Fanny; Barylyuk, Konstantin; Yang, Zhiyi; Zenobi, Renato

2014-05-21

320

Gas-phase water-mediated equilibrium between methylglyoxal and its geminal diol  

PubMed Central

In aqueous solution, aldehydes, and to a lesser extent ketones, hydrate to form geminal diols. We investigate the hydration of methylglyoxal (MG) in the gas phase, a process not previously considered to occur in water-restricted environments. In this study, we spectroscopically identified methylglyoxal diol (MGD) and obtained the gas-phase partial pressures of MG and MGD. These results, in conjunction with the relative humidity, were used to obtain the equilibrium constant, KP, for the water-mediated hydration of MG in the gas phase. The Gibbs free energy for this process, ?G°, obtained as a result, suggests a larger than expected gas-phase diol concentration. This may have significant implications for understanding the role of organics in atmospheric chemistry. PMID:20142510

Axson, Jessica L.; Takahashi, Kaito; De Haan, David O.; Vaida, Veronica

2010-01-01

321

FACTORS INFLUENCING THE DEPOSITION OF A COMPOUND THAT PARTITIONS BETWEEN GAS AND PARTICULATE PHASES  

EPA Science Inventory

How will atmospheric deposition behave for a compound when it reversibly sorbs between gas and atmospheric particulate phases? Two factors influence the answer. What physical mechanisms occur in the sorption process? What are the concentration and composition of atmospheric par...

322

GAS-PHASE OXIDATION PRODUCTS OF BIPHENYL AND POLYCHLORINATED BIPHENYLS (R825377)  

EPA Science Inventory

Our laboratory recently measured the gas-phase reaction rate constants of polychlorinated biphenyls (PCBs) with the hydroxyl radical (OH) and concluded that OH reactions are the primary removal pathway of PCBs from the atmosphere. With the reaction system previousl...

323

Gas-phase structures of molecules containing heavy p-block elements   

E-print Network

Gas-phase electron diffraction (GED) is the method of choice for determining the structures of molecules containing between two and 100 atoms, free from intermolecular interaction. However, for many molecules it becomes necessary to augment...

Wann, Derek A

324

Contraction phase of a gas-puff z-pinch  

Microsoft Academic Search

The dynamics of a gas-puff z-pinch plasma was investigated using a Kerr-cell camera. A large amplitude Rayleigh-Taylor instability was observed to develop during the contraction of the plasma. Two types of gas nozzles were examined to reduce axial nonuniformity, and it was confirmed that the uniform z-pinch was produced by the choice of the nozzle.

Kinya Moriyama; Keiichi Takasugi; Tetsu Miyamoto; Koichi Sato

1994-01-01

325

Gas phase ion\\/molecule reactions and analytical applications by tandem mass spectrometry  

Microsoft Academic Search

Fundamental studies and analytical applications by tandem mass spectrometry are described in this thesis. Gas phase ion\\/molecule reactions involving W(CO)$\\\\sb6$ and perfluorohexane (C$\\\\sb6$F$\\\\sb{14})$ are used to study mechanisms related to ion\\/surface collisions. A single collision event is suggested to be responsible for multiple fluorine atoms pick-up during collisions of tungsten-containing ions with fluorinated self-assembled monolayer surfaces. Gas phase \\

Guodong Chen

1997-01-01

326

Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species  

SciTech Connect

This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. High-resolution spectroscopy, augmented by theoretical and computational methods, is used to investigate the structure and collision dynamics of chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry. Applications and methods development are equally important experimental components of this work.

Hall,G.E.; Sears, T.J.

2009-04-03

327

T-junction separation modelling in gas–liquid two-phase flow  

Microsoft Academic Search

The principle of dynamic separation with T-junction having a horizontal run and a vertical branch is presented. The analysis of gas–liquid flow systems involving T-junctions is very important for applications to phase separation in gas–liquid transport pipelines, but the complexity of the multi dimensional phenomenon of dividing two-phase flow in T-junction needs special modelling. Based on the fundamental mass, momentum

Dionissios P. Margaris

2007-01-01

328

Gas-Phase Molecular Dynamics: High Resolution Spectroscopy and Collision Dynamics of Transient Species  

SciTech Connect

This research is carried out as part of the Gas-Phase Molecular Dynamics program in the Chemistry Department at Brookhaven National Laboratory. Chemical intermediates in the elementary gas-phase reactions involved in combustion chemistry are investigated by high resolution spectroscopic tools. Production, reaction, and energy transfer processes are investigated by transient, double resonance, polarization and saturation spectroscopies, with an emphasis on technique development and connection with theory, as well as specific molecular properties.

Hall, G.E.

2011-05-31

329

Scaling analysis of gas-liquid two-phase flow pattern in microgravity  

NASA Technical Reports Server (NTRS)

A scaling analysis of gas-liquid two-phase flow pattern in microgravity, based on the dominant physical mechanism, was carried out with the goal of predicting the gas-liquid two-phase flow regime in a pipe under conditions of microgravity. The results demonstrated the effect of inlet geometry on the flow regime transition. A comparison of the predictions with existing experimental data showed good agreement.

Lee, Jinho

1993-01-01

330

An atmospheric pressure flow reactor: Gas phase kinetics and mechanism in tropospheric conditions without wall effects  

NASA Technical Reports Server (NTRS)

A new type of gas phase flow reactor, designed to permit the study of gas phase reactions near 1 atm of pressure, is described. A general solution to the flow/diffusion/reaction equations describing reactor performance under pseudo-first-order kinetic conditions is presented along with a discussion of critical reactor parameters and reactor limitations. The results of numerical simulations of the reactions of ozone with monomethylhydrazine and hydrazine are discussed, and performance data from a prototype flow reactor are presented.

Koontz, Steven L.; Davis, Dennis D.; Hansen, Merrill

1988-01-01

331

Formation of complex organic molecules in cold objects: the role of gas-phase reactions  

NASA Astrophysics Data System (ADS)

While astrochemical models are successful in reproducing many of the observed interstellar species, they have been struggling to explain the observed abundances of complex organic molecules. Current models tend to privilege grain surface over gas-phase chemistry in their formation. One key assumption of those models is that radicals trapped in the grain mantles gain mobility and react on lukewarm ( ? 30 K) dust grains. Thus, the recent detections of methyl formate (MF) and dimethyl ether (DME) in cold objects represent a challenge and may clarify the respective role of grain-surface and gas-phase chemistry. We propose here a new model to form DME and MF with gas-phase reactions in cold environments, where DME is the precursor of MF via an efficient reaction overlooked by previous models. Furthermore, methoxy, a precursor of DME, is also synthesized in the gas phase from methanol, which is desorbed by a non-thermal process from the ices. Our new model reproduces fairly well the observations towards L1544. It also explains, in a natural way, the observed correlation between DME and MF. We conclude that gas-phase reactions are major actors in the formation of MF, DME and methoxy in cold gas. This challenges the exclusive role of grain-surface chemistry and favours a combined grain-gas chemistry.

Balucani, Nadia; Ceccarelli, Cecilia; Taquet, Vianney

2015-04-01

332

Generalized average of signals (GAS) - a new method for denoising and phase detection  

Microsoft Academic Search

A novel method called Generalized Average of Signals (GAS) was developed and tested during the last two years (Málek et al., in press). This method is designed for processing of seismograms from dense seismic arrays and is convenient mainly for denoising and weak phase detection. The main idea of the GAS method is based on non-linear stacking of seismograms in

J. Malek; P. Kolinsky; J. Strunc; J. Valenta

2007-01-01

333

Two-fluid model for a rotating trapped Fermi gas in the BCS phase  

Microsoft Academic Search

We investigate the dynamical properties of a superfluid gas of trapped fermionic atoms in the BCS phase. As a simple example we consider the reaction of the gas to a slow rotation of the trap. It is shown that the currents generated by the rotation can be understood within a two-fluid model similar to the one used in the theory

Michael Urban

2005-01-01

334

DEMONSTRATION BULLETIN: GAS-PHASE CHEMICAL REDUCTION - ECO LOGIC INTERNATIONAL, INC.  

EPA Science Inventory

The patented Eco Logic Process employs a gas-phase reduction reaction of hydrogen with organic and chlorinated organic compounds at elevated temperatures to convert aqueous and oily hazardous contaminants into a hydrocarbon-rich gas product. After passing through a scrubber, the ...

335

APPLICATIONS ANALYSIS REPORT: ECO LOGIC INTERNATIONAL GAS-PHASE CHEMICAL REDUCTION PROCESS - THE REACTOR SYSTEM  

EPA Science Inventory

This report details the Superfund Innovative Technology Evaluation of Eco Logic International's gas-phase chemical reduction process, with an emphasis on their Reactor System. he Eco Logic process employees a high temperature reactor filled with hydrogen gas as the means to destr...

336

Gas phase dispersion in compost as a function of different water contents and air flow rates  

Microsoft Academic Search

Gas phase dispersion in a natural porous medium (yard waste compost) was investigated as a function of gas flow velocity and compost volumetric water content using oxygen and nitrogen as tracer gases. The compost was chosen because it has a very wide water content range and because it represents a wide range of porous media, including soils and biofilter media.

Prabhakar Sharma; Tjalfe G. Poulsen

2009-01-01

337

Evaluated Gas Phase Basicities and Proton Affinities of Molecules: An Update  

Microsoft Academic Search

The available data on gas-phase basicities and proton affinities of approximately 1700 molecular, radical and atomic neutral species are evaluated and compiled. Tables of the data are sorted (1) according to empirical formula and (2) according to evaluated gas basicity. This publication constitutes an update of a similar evaluation published in 1984.

Edward P. L. Hunter; Sharon G. Lias

1998-01-01

338

Supporting Information First detection of methylgermylene in the gas-phase and time resolved study of  

E-print Network

1 Supporting Information First detection of methylgermylene in the gas-phase and time resolved anhydrous magnesium sulphate, filtered, and the solvent removed by distillation. Vacuum distillation as reference. Low resolution mass spectra were determined by GC/MS, using a Hewlett-Packard 5890II gas

Leigh, William J.

339

SPATIAL DISTRIBUTION OF GAS AND SOLID PHASES IN CONICAL SLURRY BUBBLE COLUMNS  

Microsoft Academic Search

In this work we perform an experimental study of the spatial distribution of phases in slurry bubble columns with conical distributors that have a volume comparable to that of the cylindrical section. Three different distributors were used whose apex angles were 13°, 22° and 34°. In gas-liquid operation, the gas holdups are axially uniform in the cylindrical section and decrease

S. SIQUIER; A. RONCHETTI; M. CALDERÓN; P. LLAGUNO; A. E. SÁEZ

1997-01-01

340

Two-dimensional two-phase gas-liquid flow. I - Flow patterns  

NASA Astrophysics Data System (ADS)

Two-dimensional gas-liquid flows can appear in various structures such as petroleum or geothermal fissured reservoirs and heat transfer devices. The present work describes the flow patterns observed when the surface velocities of the gas and liquid phases as well as the inclination vary. Flow patterns for horizontal flow are presented.

Kouame, Seraphin; Piquemal, Jean; Bories, Serge

1991-08-01

341

NAT nucleation and denitrification in the polar stratosphere  

NASA Astrophysics Data System (ADS)

Nitric acid trihydrate (NAT) particles in the polar stratosphere are known to influence the chemistry of ozone depletion. NAT particles, along with other liquid and crystalline particles, provide heterogeneous surfaces for chlorine activation. More importantly, they can take up significant amounts of HNO3 from the gas phase and transport HNO3 downward by sedimentation. This can lead to denitrification, in the Arctic typically at altitudes above about 20 km, and a re-nitrification below, at the level where the NAT particles evaporate. The nucleation rate of NAT particles is a critical parameter for the simulation of this process. Very low NAT nucleation rates around 2?10-9cm-3s-1 have been deduced for low NAT supersaturations from observations. In previous studies, vertical HNO3 transport has been successfully simulated by Lagrangian 3-D simulations using a constant NAT nucleation rate of around 2?10-9cm-3s-1, for the Arctic winters in the years 2003 and 2005. However, for winter 2009/2010, this approach does not generate satisfying results. Here, saturation dependent NAT nucleation rates were derived from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), observations under the assumption that NAT nucleates heterogeneously on dust particles that are characterized by active sites with a certain occurrence probability distribution depending on the contact angle. Simulations with the Zurich Optical and Microphysical box Model (ZOMM) along back-trajectories starting from points where PSCs were observed by CALIPSO allow the parametrisation of heterogeneous nucleation rates for NAT and ice on dust, and the reproduction of the different PSC classes observed. We present simulations by the Chemical Lagrangian Model of the Stratosphere (CLaMS) of the winter 2009/2010 applying this new parametrisation of heterogeneous NAT nucleation rates. The CLaMS simulation is initialized using a combination of MLS, MIPAS-ENVISAT and ACE-FTS data. The simulation shows good agreement of chemical trace species with observations, especially H2O and HNO3, which are important for the reliable simulation of HNO3 supersaturations over NAT. This is shown by comparisons with in-situ CFH frost point hygrometer sondes and satellite based observations of H2O and HNO3 by MIPAS-ENVISAT, MLS, and ACE-FTS. Comparisons of the size distribution of the simulated NAT particles with the observations by a Forward Scattering Spectrometer Probe (FSSP) aboard the high-flying research aircraft Geophysica operated in the winter 2009/2010 indicate good agreement, even though the largest observed particles are not reproduced by the simulation. The simulation also reproduces the HNO3 redistribution in the Arctic winter 2009/2010 with denitrification and the re-nitrification peaks as observed by the ACE-FTS satellite instrument and in-situ observations by the SIOUX instrument operated aboard Geophysica.

Grooß, Jens-Uwe; Engel, Ines; Hoyle, Christopher R.; Luo, Beiping; Peter, Thomas; Frey, Wiebke; Molleker, Sergej; Borrmann, Stephan; Schlager, Hans; Vömel, Holger; Kivi, Rigel; Walker, Kaley A.; Santee, Michelle L.; Stiller, Gabriele; Pitts, Michael; Müller, Rolf

2013-04-01

342

Nucleation in Synoptically Forced Cirrostratus  

NASA Technical Reports Server (NTRS)

Formation and evolution of cirrostratus in response to weak, uniform and constant synoptic forcing is simulated using a one-dimensional numerical model with explicit microphysics, in which the particle size distribution in each grid box is fully resolved. A series of tests of the model response to nucleation modes (homogeneous-freezing-only/heterogeneous nucleation) and heterogeneous nucleation parameters are performed. In the case studied here, nucleation is first activated in the prescribed moist layer. A continuous cloud-top nucleation zone with a depth depending on the vertical humidity gradient and one of the nucleation parameters is developed afterward. For the heterogeneous nucleation cases, intermittent nucleation zones in the mid-upper portion of the cloud form where the relative humidity is on the rise, because existent ice crystals do not uptake excess water vapor efficiently, and ice nuclei (IN) are available. Vertical resolution as fine as 1 m is required for realistic simulation of the homogeneous-freezing-only scenario, while the model resolution requirement is more relaxed in the cases where heterogeneous nucleation dominates. Bulk microphysical and optical properties are evaluated and compared. Ice particle number flux divergence, which is due to the vertical gradient of the gravity-induced particle sedimentation, is constantly and rapidly changing the local ice number concentration, even in the nucleation zone. When the depth of the nucleation zone is shallow, particle number concentration decreases rapidly as ice particles grow and sediment away from the nucleation zone. When the depth of the nucleation zone is large, a region of high ice number concentration can be sustained. The depth of nucleation zone is an important parameter to be considered in parametric treatments of ice cloud generation.

Lin, R.-F.; Starr, D. OC.; Reichardt, J.; DeMott, P. J.

2004-01-01

343

Non-LTE dust nucleation in sub-saturated vapors  

E-print Network

We use the kinetic theory of nucleation to explore the properties of dust nucleation in sub-saturated vapors. Due to radiation losses, the sub-critical clusters have a smaller temperature compared to their vapor. This alters the dynamical balance between attachment and detachment of monomers, allowing for stable nucleation of grains in vapors that are sub-saturated for their temperature. We find this effect particularly important at low densities and in the absence of a strong background radiation field. We find new conditions for stable nucleation in the n-T phase diagram. The nucleation in the non-LTE regions is likely to be at much slower rate than in the super-saturated vapors. We evaluate the nucleation rate, warning the reader that it does depend on poorly substantiated properties of the macro-molecules assumed in the computation. On the other hand, the conditions for nucleation depend only on the properties of the large stable grains and are more robust. We finally point out that this mechanism may be relevant in the early universe as an initial dust pollution mechanism, since once the interstellar medium is polluted with dust, mantle growth is likely to be dominant over non-LTE nucleation in the diffuse medium.

Davide Lazzati

2007-11-09

344

Investigations into the fundamentals of gas-phase and gas-surface chemistry prevalent in growth of  

E-print Network

Filament (HF) and microwave plasma enhanced chemical vapour deposition (CVD) reactors used for depositing of C2 rotational temperature show the plasma temperature to be 3520 ± 260 K and C2(a, v=0) column influence on the gas-phase BHx concen- trations. A high pressure CVD microwave reactor has been installated

Bristol, University of

345

Crystallization and nucleation kinetics in volcanic systems  

NASA Astrophysics Data System (ADS)

The main objective of this experimental study is to constrain and quantitatively model the complex solidification process that transforms a magma in a solid material. Of major interest are crystal nucleation and growth driven by isothermal decompression of hydrous magmas, and comparison with results from more abundant crystal growth/nucleation data obtained in isobaric cooling experiments. This research concerns two different volcanic systems, Pantelleria (peralkaline rhyolite) and Stromboli (basalt), to better understand how crystallization kinetics can affect different magma compositions. For Stromboli volcanic system TZM apparatus has been used to perform decompression runs at Bayerisches Geoinstitut in Bayreuth (DE). As for Pantelleria composition, cooling experiments has been done using IHPV devices at ISTO of Orléans (FR), on the basis of previous phase equilibrium work (Di Carlo et al., 2010). First obtained results for Stromboli case show high rates of nucleation and crystal growth during the initial stages of crystallization which were followed by crystal growth at approximately constant number densities as equilibrium was approached. Shapes of crystals growing in melts are controlled by the kinetics of crystallization and may provide information about the degree of undercooling experienced by batches of magma en route to the surface (Lofgren, 1980). The study of crystallization kinetics through phases growth rates (Couch et al., 2003), together with the calculation of nucleation density and nucleation rates (Hammer et al., 1999) represent a step toward the estimation of the time scales of magmatic processes in volcanic systems and the interpretation of shallow magmatic processes. The results for Stromboli suggest average crystal growth timescales on the order of weeks, but this is complicated by clear evidence that some crystals have experienced repeated periods of both dissolution and growth (Landi et al., 2004).

Agostini, C.; Fortunati, A.; Carroll, M. R.; Scaillet, B.; Landi, P.

2011-12-01

346

Biofiltration of mixtures of gas-phase styrene and acetone with the fungus Sporothrix variecibatus  

Microsoft Academic Search

The biodegradation performance of a biofilter, inoculated with the fungus Sporothrix variecibatus, to treat gas-phase styrene and acetone mixtures under steady-state and transient conditions was evaluated. Experiments were carried out by varying the gas-flow rates (0.05–0.4m3h?1), leading to empty bed residence times as low as 17.1s, and by changing the concentrations of gas-phase styrene (0.01–6.3gm?3) and acetone (0.01–8.9gm?3). The total

Eldon R. Rene; Radka Špa?ková; María C. Veiga; Christian Kennes

2010-01-01

347

Control of gas phase nanoparticle shape and its effect on MRI relaxivity  

NASA Astrophysics Data System (ADS)

We have used a sputtering gas aggregation source to produce Fe@FeO nanoparticles with different shapes, by annealing them at different temperatures in the gas phase. Without annealing, the most common shape found for the nanoparticles is cubic but annealing the nanoparticles at 1129 °C transforms the cubes into cuboctahedra. Measurements of the MRI relaxivity show that the cubic nanoparticles have a higher performance by a factor of two, which is attributed to a higher saturation magnetization for this shape. This indicates that the shape-control enabled by gas-phase synthesis is important for obtaining optimal performance in applications.

Akta?, S?tk?; Thornton, Stuart C.; Binns, Chris; Lari, Leonardo; Pratt, Andrew; Kröger, Roland; Horsfield, Mark A.

2015-03-01

348

Flow Rate Measurement of Oil\\/Gas\\/Water Three-Phase Flow with V-Cone Flow Meter  

Microsoft Academic Search

Mass flow rate is an important parameter of oil\\/gas\\/water three-phase flow, most multi-phase flow meters are based on the measurement of total mass flow rate and phase fraction. As the Reynolds number of three-phase flow grows to a certain number, the oil and water phase are considered as a homogenous mixture with a mixed density. In this case, oil\\/gas\\/water three-phase

F. S. Zhang; F. Dong

2010-01-01

349

Methane-to-Methanol Conversion by Gas-Phase Transition Metal Oxide Cations: Experiment and Theory  

E-print Network

Methane-to-Methanol Conversion by Gas-Phase Transition Metal Oxide Cations: Experiment and Theory-phase transition metal oxide cations can convert methane to methanol. Methane activation by MO+ is discussed such as methanol has attracted great experimental and theoretical interest due to its importance as an industrial

Metz, Ricardo B.

350

ANALYSIS OF A GAS-PHASE PARTITIONING TRACER TEST CONDUCTED THROUGH FRACTURED MEDIA  

EPA Science Inventory

The gas-phase partitioning tracer method was used to estimate non-aqueous phase liquid (NAPL), water, and air saturations in the vadose zone at a chlorinated-solvent contaminated field site in Tucson, AZ. The tracer test was conducted in a fractured clay system that is the confin...

351

Partitioning of semivolatile surface-active compounds between bulk, surface and gas phase  

Microsoft Academic Search

We present a model study demonstrating that surface partitioning of volatile surfactants enhances their uptake by submicron liquid droplets. In submicron-sized droplets, surface partitioning of a surface-active volatile species may significantly decrease its equilibrium partial pressure, thus increasing the total flux of the surfactant from gas phase to aqueous phase. Such uptake of volatile organic species into aqueous aerosols can

S. Romakkaniemi; H. Kokkola; J. N. Smith; N. L. Prisle; A. N. Schwier; V. F. McNeill; A. Laaksonen

2011-01-01

352

Small gas-phase dianions produced by sputtering and gas flooding  

SciTech Connect

We have extended our previous experiment [Schauer et al., Phys. Rev. Lett. 65, 625 (1990)] where we had produced small gas-phase dianion clusters of C{sub n}{sup 2-}(n{>=}7) by means of sputtering a graphite surface by Cs{sup +} ion bombardment. Our detection sensitivity for small C{sub n}{sup 2-} could now be increased by a factor of about 50 for odd n. Nevertheless, a search for the elusive pentamer dianion of C{sub 5}{sup 2-} was not successful. As an upper limit, the sputtered flux of C{sub 5}{sup 2-} must be at least a factor of 5000 lower than that of C{sub 7}{sup 2-}, provided that the lifetime of C{sub 5}{sup 2-} is sufficiently long to allow its detection by mass spectrometry. When oxygen gas (flooding with either O{sub 2} or with N{sub 2}O) was supplied to the Cs{sup +}-bombarded graphite surface, small dianions of OC{sub n}{sup 2-}(5{<=}n{<=}14) and O{sub 2}C{sub 7}{sup 2-} were observed in addition to C{sub n}{sup 2-}(n{>=}7). Similarly, Cs{sup +} sputtering of graphite with simultaneous SF{sub 6} gas flooding produced SC{sub n}{sup 2-}(6{<=}n{<=}18). Mixed nitrogen-carbon or fluorine-carbon dianion clusters could not be observed by these means. Attempts to detect mixed metal-fluoride dianions for SF{sub 6} gas flooding of various Cs{sup +}-bombarded metal surfaces were successful for the case of Zr, where metastable ZrF{sub 6}{sup 2-} was observed. Cs{sup +} bombardment of a silicon carbide (SiC) wafer produced SiC{sub n}{sup 2-} (n=6,8,10). When oxygen gas was supplied to the Cs{sup +}-bombarded SiC surface, small dianions of SiOC{sub n}{sup 2-} (n=4,6,8) and of SiO{sub 2}C{sub n}{sup 2-} (n=4,6) as well as a heavier unidentified dianion (at m/z=98.5) were observed. For toluene (C{sub 7}H{sub 8}) vapor flooding of a Cs{sup +}-bombarded graphite surface, several hydrocarbon dianion clusters of C{sub n}H{sub m}{sup 2-}(n{>=}7) were produced in addition to C{sub n}{sup 2-}(n{>=}7), while smaller C{sub n}H{sub m}{sup 2-} with n{<=}6 could not be observed. BeC{sub n}{sup 2-} (n=4,6,8,10), Be{sub 2}C{sub 6}{sup 2-}, as well as BeC{sub 8}H{sub m}{sup 2-} (with m=2 and/or m=1) were observed for toluene vapor flooding of a Cs{sup +}-bombarded beryllium metal foil. The metastable pentamer {sup 9}Be{sup 12}C{sub 4}{sup 2-} at m/z=28.5 was the smallest and lightest dianion molecule that we could detect. The small dianion clusters of SC{sub n}{sup 2-}, OC{sub n}{sup 2-}, BeC{sub n}{sup 2-}, and SiO{sub m}C{sub n}{sup 2-} (m=0,1,2) have different abundance patterns. A resemblance exists between the abundance patterns of BeC{sub n}{sup 2-} and SiC{sub n}{sup 2-}, even though calculated molecular structures of BeC{sub 6}{sup 2-} and SiC{sub 6}{sup 2-} are different. The abundance pattern of SC{sub n}{sup 2-} is fairly similar to that of C{sub n}{sup 2-}.

Franzreb, Klaus; Williams, Peter [Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287 (United States)

2005-12-08

353

On the Ice Nucleation Spectrum  

NASA Technical Reports Server (NTRS)

This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.

Barahona, D.

2012-01-01

354

Pre-nucleation clusters as solute precursors in crystallisation.  

PubMed

Crystallisation is at the heart of various scientific disciplines, but still the understanding of the molecular mechanisms underlying phase separation and the formation of the first solid particles in aqueous solution is rather limited. In this review, classical nucleation theory, as well as established concepts of spinodal decomposition and liquid-liquid demixing, is introduced together with a description of the recently proposed pre-nucleation cluster pathway. The features of pre-nucleation clusters are presented and discussed in relation to recent modifications of the classical and established models for phase separation, together with a review of experimental work and computer simulations on the characteristics of pre-nucleation clusters of calcium phosphate, calcium carbonate, iron(oxy)(hydr)oxide, silica, and also amino acids as an example of small organic molecules. The role of pre-nucleation clusters as solute precursors in the emergence of a new phase is summarized, and the link between the chemical speciation of homogeneous solutions and the process of phase separation via pre-nucleation clusters is highlighted. PMID:24457316

Gebauer, Denis; Kellermeier, Matthias; Gale, Julian D; Bergström, Lennart; Cölfen, Helmut

2014-04-01

355

Phenolic oxime copper complexes: a gas phase investigation   

E-print Network

This thesis explores the use of mass spectrometry to define the strengths, and understand solution phase speciation of phenolic oxime-based solvent extractants of the types used in the hydrometallurgical recovery of ...

Roach, Benjamin David

2011-06-27

356

NANOMATERIAL SOLUTIONS FOR HOT COAL GAS CLEANUP - PHASE I  

EPA Science Inventory

Integrated gasification combined cycle (IGCC) is a new coal gasification technique that efficiently uses the hot (900-1500°C) generated syngas to power both steam and gas turbines. Due to regulations, this syngas must be free of sulfur and purification is normally carried ...

357

AN ADVANCED FLUE GAS MONITOR FOR SO2 - PHASE I  

EPA Science Inventory

The development of an instrument for continuously monitoring SO2 levels in flue gas is proposed. The SO2 will be detected by means of an electrochemical sensor cell, which operates in a three-electrode potentiostatic mode. The proposed innovation is develop-ment of an advan...

358

Ceramic stationary gas turbine development. Final report, Phase 1  

SciTech Connect

This report summarizes work performed by Solar Turbines Inc. and its subcontractors during the period September 25, 1992 through April 30, 1993. The objective of the work is to improve the performance of stationary gas turbines in cogeneration through implementation of selected ceramic components.

NONE

1994-09-01

359

Competitive nucleation in reversible probabilistic cellular automata.  

PubMed

The problem of competitive nucleation in the framework of probabilistic cellular automata is studied from the dynamical point of view. The dependence of the metastability scenario on the self-interaction is discussed. An intermediate metastable phase, made of two flip-flopping chessboard configurations, shows up depending on the ratio between the magnetic field and the self-interaction. A behavior similar to the one of the stochastic Blume-Capel model with Glauber dynamics is found. PMID:18999368

Cirillo, Emilio N M; Nardi, Francesca R; Spitoni, Cristian

2008-10-01

360

Organic hydrogen gas sensor with palladium-coated ?-phase poly(vinylidene fluoride) thin films  

NASA Astrophysics Data System (ADS)

We have proposed an organic hydrogen gas sensor in which palladium (Pd)-coated ?-phase poly(vinylidene fluoride) (PVDF) films are utilized. Volume expansion of the Pd thin film caused by absorption of hydrogen gas is monitored by a piezoelectric thin film of PVDF attached to the Pd films. We have developed a simple method of synthesizing ?-phase PVDF films from ?-phase PVDF powder by using a wet process in which a mixture of acetone and hexamethylphosphoric triamide is used as the solvent for the PVDF powder. The sensor works by itself at room temperature without a power source.

Imai, Yuji; Kimura, Yasuo; Niwano, Michio

2012-10-01

361

Dynamic damage nucleation and evolution in multiphase materials  

NASA Astrophysics Data System (ADS)

For ductile metals, dynamic fracture occurs through void nucleation, growth, and coalescence. Previous experimental works in high purity metals have shown that microstructural features such as grain boundaries, inclusions, vacancies, and heterogeneities can act as initial void nucleation sites. However, for materials of engineering significance, those with, second phase particles it is less clear what the role of a soft second phase will be on damage nucleation and evolution. To approach this problem in a systematic manner, two materials have been investigated: high purity copper and copper with 1% lead. These materials have been shock loaded at ˜1.5 GPa and soft recovered. In-situ free surface velocity information and post mortem metallography reveals the presence of a high number of small voids in CuPb in comparison to a lower number of large voids in Cu. This suggests that damage evolution is nucleation dominated in the CuPb and growth dominated in the pure Cu.

Fensin, S. J.; Escobedo, J. P.; Gray, G. T.; Patterson, B. M.; Trujillo, C. P.; Cerreta, E. K.

2014-05-01

362

Polymer crystal-melt interfaces and nucleation in polyethylene  

E-print Network

Kinetic barriers cause polymers to crystallize incompletely, into nanoscale lamellae interleaved with amorphous regions. As a result, crystalline polymers are full of crystal-melt interfaces, which dominate their physical properties. The longstanding theoretical challenge to understand these interfaces has new relevance, because of accumulating evidence that polymer crystals often nucleate via a metastable, partially ordered "rotator" phase. To test this idea requires a theory of the bulk and interfacial free energies of the critical nucleus. We present a new approach to the crystal-melt interface, which represents the amorphous region as a grafted brush of loops in a self-consistent pressure field. We combine this theory with estimates of bulk free energy differences, to calculate nucleation barriers and rates via rotator versus crystal nuclei for polyethylene. We find rotator-phase nucleation is indeed favored throughout the temperature range where nucleation is observed. Our methods can be extended to other polymers.

Scott T. Milner

2010-09-22

363

Development and Evaluation of Gold-Centered Monolayer Protected Nanoparticle Stationary Phases for Gas Chromatography  

SciTech Connect

The current status for the development of novel open-tubular gas chromatography (GC) stationary phases consists of thin films of gold-centered monolayer protected nanoparticles (MPNs) is reported. Dodecanethiol MPNs, in which the monolayer is dodecanethiol linked to the gold nanoparticle, have shown great promise as a GC stationary phase with efficient columns having been produced in a variety of capillary i.d.'s with stationary phase film depths ranging from 10-60 nm, +/- 2 nm at a given film depth. Stationary phase operational parameters are discussed including maximum operating temperature, sample capacity, and stationary phase lifetime and robustness.

Gross, Gwen M.; Grate, Jay W.; Synovec, Robert E.

2004-12-10

364

Fragmentation and the Bose-glass phase transition of the disordered one-dimensional Bose gas  

SciTech Connect

We investigate the superfluid-insulator quantum phase transition in a disordered one-dimensional Bose gas in the mean-field limit by studying the probability distribution of the density. The superfluid phase is characterized by a vanishing probability to have zero density, whereas a nonzero probability marks the insulator phase. This relation is derived analytically and confirmed by a numerical study. This fragmentation criterion is particularly suited for detecting the phase transition in experiments. When a harmonic trap is included, the transition to the insulating phase can be extracted from the statistics of the local density distribution.

Fontanesi, Luca; Wouters, Michiel; Savona, Vincenzo [Institute of Theoretical Physics, Ecole Polytechnique Federale de Lausanne EPFL, CH-1015 Lausanne (Switzerland)

2011-03-15

365

Possible links between the liquid-gas and deconfinement-hadronization phase transitions  

E-print Network

It is commonly accepted that strongly interacting matter has several phase transitions in different domains of temperature and baryon density. In this contribution I discuss two most popular phase transitions which in principle can be accessed in nuclear collisions. One of them, the liquid-gas phase transition, is well established theoretically and studied experimentally in nuclear multifragmentation reactions at intermediate energies. The other one, the deconfinement-hadronization phase transition, is at the focus of present and future experimental studies with relativistic heavy-ion beams at SPS, RHIC and LHC. Pssible links between these two phase transitions are identified from the viewpoint of their manifestation in violent nuclear collisions.

I. N. Mishustin

2006-09-19

366

Two-phase turbine engines. [using gas-liquid mixture accelerated in nozzles  

NASA Technical Reports Server (NTRS)

A description is given of a two-phase turbine which utilizes a uniform mixture of gas and liquid accelerated in nozzles of the types reported by Elliott and Weinberg (1968). The mixture acts directly on an axial flow or tangential impulse turbine or is separated into gas and liquid streams which operate separately on a gas turbine and a hydraulic turbine. The basic two-phase cycles are examined, taking into account working fluids, aspects of nozzle expansion, details of turbine cycle operation, and the effect of mixture ratio variation. Attention is also given to two-phase nozzle efficiency, two-phase turbine operating characteristics and efficiencies, separator turbines, and impulse turbine experiments.

Elliott, D. G.; Hays, L. G.

1976-01-01

367

Lipase hydration state in the gas phase: Sorption isotherm measurements and inverse gas chromatography.  

E-print Network

chromatography. Zsuzsanna Marton1 , Ludovic Chaput1 , Guillaume Pierre1 and Marianne Graber1 1 Université de la Rochelle, Cedex 01, France. Keywords: Water, Lipase, Adsorption, Inverse Gas Chromatography, Solid@univ-lr.fr Fax : +33 5 46 45 82 65 Abbreviations: IGC, Inverse Gas Chromatography aW, water thermodynamic

Paris-Sud XI, Université de

368

Deposition nucleation viewed as homogeneous or immersion freezing in pores and cavities  

NASA Astrophysics Data System (ADS)

Heterogeneous ice nucleation is an important mechanism for the glaciation of mixed phase clouds and may also be relevant for cloud formation and dehydration at the cirrus cloud level. It is thought to proceed through different mechanisms, namely contact, condensation, immersion and deposition nucleation. Supposedly, deposition nucleation is the only pathway which does not involve liquid water but occurs by direct water vapor deposition on a surface. This study challenges this classical view by putting forward the hypothesis that what is called deposition nucleation is in fact homogeneous or immersion nucleation occurring in pores and cavities that may form between aggregated primary particles and fill with water at relative humidity RHw < 100% because of the inverse Kelvin effect. Evidence for this hypothesis of pore condensation and freezing (PCF) originates from a number of only loosely connected scientific areas. The prime example for PCF is ice nucleation in clay minerals and mineral dusts, for which the data base is best. Studies on freezing in confinement carried out on mesoporous silica materials such as SBA-15, SBA-16, MCM-41, zeolites and KIT have shown that homogeneous ice nucleation occurs abruptly at T=230-235 K in pores with diameters (D) of 3.5-4 nm or larger but only gradually at T=210-230 K in pores with D=2.5-3.5 nm. Melting temperatures in pores are depressed by an amount that can be described by the Gibbs-Thomson equation. Water adsorption isotherms of MCM-41 show that pores with D=3.5-4 nm fill with water at RHw = 56-60% in accordance with an inverse Kelvin effect. Water in such pores should freeze homogeneously for T < 235 K even before relative humidity with respect to ice (RHi) reaches ice saturation. Ice crystal growth by water vapor deposition from the gas phase is therefore expected to set in as soon as RHw > 100%. Pores with D > 7.5 nm fill with water at RHi > 100% for T < 235 K and are likely to freeze homogeneously as soon as they are filled with water. Water in pores can freeze in immersion mode at T > 235 K if the pore walls contain an active site. Pore analysis of clay minerals shows that kaolinites exhibit pore structures with pore diameters of 20-50 nm. The mesoporosity of illites and montmorillonites is characterized by pores with T = 2-5 nm. The number and size of pores is distinctly increased in acid treated montmorillonites like K10. Many clay minerals and mineral dusts show a strong increase in ice nucleation efficiency when temperature is decreased below 235 K. Such an increase is difficult to explain when ice nucleation is supposed to occur by a deposition mechanism, but evident when assuming freezing in pores, because for homogeneous ice nucleation only small pore volumes are needed, while heterogeneous ice nucleation requires larger pore structures to contain at least one active site for immersion nucleation. Together, these pieces of evidence strongly suggest that ice nucleation within pores should be the prevailing freezing mechanism of clay minerals for RHw below water saturation. Extending the analysis to other types of ice nuclei shows that freezing in pores and cracks is probably the prevailing ice nucleation mechanism for glassy and volcanic ash aerosols at RHw below water saturation. Freezing of water in carbon nanotubes might be of significance for ice nucleation by soot aerosols. No case could be identified that gives clear evidence of ice nucleation by water vapor deposition on a solid surface. Inspection of ice nuclei with a close lattice match to ice, such as silver iodide or SnomaxTM, show that for high ice nucleation efficiency below water saturation the presence of impurities or cracks on the surface may be essential. Soluble impurities promote the formation of a liquid phase below water saturation in patches on the surface or as a complete surface layer that offers an environment for immersion freezing. If porous aerosol particles come in contact with semivolatile vapors, these will condense preferentially in pores before a coating on

Marcolli, C.

2013-06-01

369

Nucleation of silicon nanocrystals in a remote plasma without subsequent coagulation  

NASA Astrophysics Data System (ADS)

We report on the growth mechanism of spherical silicon nanocrystals in a remote expanding Ar plasma using a time-modulated SiH4 gas injection in the microsecond time range. Under identical time-modulation parameters, we varied the local density of the SiH4 gas by changing its stagnation pressure on the injection line over the range of 0.1-2.0 bar. We observed that nanocrystals were synthesized in a size range from ˜2 to ˜50 nm with monocrystalline morphology. Smaller nanocrystals (˜2-6 nm) with narrower size distributions and with higher number densities were synthesized with an increase of the SiH4 gas-phase density. We related this observation to the rapid depletion of the number density of the molecules, ions, and radicals in the plasma during nanocrystal growth, which can primarily occur via nucleation with no significant subsequent coagulation. In addition, in our remote plasma environment, rapid cooling of the gas in the particle growth zone from ˜1500 to ˜400 K significantly reduces the coalescence rate of the nanoparticles, which makes the coagulation process highly unlikely. Our observations on nanocrystal formation via nucleation indicated that subsequent coagulation for further growth is not always an essential step on nanoparticle formation.

Do?an, Ilker; Weeks, Stephen L.; Agarwal, Sumit; van de Sanden, Mauritius C. M.

2014-06-01

370

Liquid to solid nucleation via onion structure droplets  

NASA Astrophysics Data System (ADS)

We study homogeneous nucleation from a deeply quenched metastable liquid to a spatially modulated phase. We find, for a general class of density functional theories, that the universally favored nucleating droplet in dimensions d ? 3 is spherically symmetric with radial modulations resembling the layers of an onion. The existence of this droplet has important implications for systems with effective long-range interactions, and potentially applies to polymers, plasmas, and metals.

Barros, Kipton; Klein, W.

2013-11-01

371

Two-color experiments in the gas phase at FLASH  

Microsoft Academic Search

Intense ultra-short XUV-pulses from the Free Electron Laser in Hamburg (FLASH) were used in combination with the synchronized near-infrared (NIR) radiation from a femtosecond laser to perform two-color experiments on rare gas atoms and small molecules. Results of atomic photoionization in the presence of a NIR dressing field are presented and discussed for the low field regime, i.e. for intensities

M. Meyer; D. Cubaynes; J. Dardis; P. Hayden; P. Hough; V. Richardson; E. T. Kennedy; J. T. Costello; S. Düsterer; W. B. Li; P. Radcliffe; H. Redlin; J. Feldhaus; S. I. Strakhova; E. V. Gryzlova; A. N. Grum-Grzhimailo; R. Taïeb; A. Maquet

2010-01-01

372

Experimental study on liquid\\/solid phase change for cold energy storage of Liquefied Natural Gas (LNG) refrigerated vehicle  

Microsoft Academic Search

The present paper addresses an experimental investigation of the cold storage with liquid\\/solid phase change of water based on the cold energy recovery of Liquefied Natural Gas (LNG) refrigerated vehicles. Water as phase change material (PCM) was solidified outside the heat transfer tubes that were internally cooled by cryogenic nitrogen gas substituting cryogenic natural gas. The ice layer profiles were

Hongbo Tan; Yanzhong Li; Hanfei Tuo; Man Zhou; Baocong Tian

2010-01-01

373

Investigation into the determination of trimethylarsine in natural gas and its partitioning into gas and condensate phases using (cryotrapping)\\/gas chromatography coupled to inductively coupled plasma mass spectrometry and liquid\\/solid sorption techniques  

Microsoft Academic Search

Speciation of trialkylated arsenic compunds in natural gas, pressurized and stable condensate samples from the same gas well was performed using (Cryotrapping) Gas Chromatography-Inductively Coupled Plasma Mass Spectrometry. The major species in all phases investigated was found to be trimethylarsine with a highest concentration of 17.8 ng\\/L (As) in the gas phase and 33.2 ?g\\/L (As) in the stable condensate phase. The

E. M. Krupp; C. Johnson; C. Rechsteiner; M. Moir; D. Leong; J. Feldmann

2007-01-01

374

Surface Nanobubbles Nucleate Microdroplets  

NASA Astrophysics Data System (ADS)

When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability.

Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef

2014-04-01

375

Experimental evidence for seismically initiated gas bubble nucleation and growth in groundwater as a mechanism for coseismic borehole water level rise and remotely triggered seismicity  

NASA Astrophysics Data System (ADS)

Changes in borehole water levels and remotely triggered seismicity occur in response to near and distant earthquakes at locations around the globe, but the mechanisms for these phenomena are not well understood. Experiments were conducted to show that seismically initiated gas bubble growth in groundwater can trigger a sustained increase in pore fluid pressure consistent in magnitude with observed coseismic borehole water level rise, constituting a physically plausible mechanism for remote triggering of secondary earthquakes through the reduction of effective stress in critically loaded geologic faults. A portion of the CO2 degassing from the Earth's crust dissolves in groundwater where seismic Rayleigh and P waves cause dilational strain, which can reduce pore fluid pressure to or below the bubble pressure, triggering CO2 gas bubble growth in the saturated zone, indicated by a spontaneous buildup of pore fluid pressure. Excess pore fluid pressure was measured in response to the application of 0.1-1.0 MPa, 0.01-0.30 Hz confining stress oscillations to a Berea sandstone core flooded with initially subsaturated aqueous CO2, under conditions representative of a confined aquifer. Confining stress oscillations equivalent to the dynamic stress of the 28 June 1992 Mw 7.3 Landers, California, earthquake Rayleigh wave as it traveled through the Long Valley caldera, and Parkfield, California, increased the pore fluid pressure in the Berea core by an average of 36 ± 15 cm and 23 ± 15 cm of equivalent freshwater head, respectively, in agreement with 41.8 cm and 34 cm rises recorded in wells at those locations.

Crews, Jackson B.; Cooper, Clay A.

2014-09-01

376

Formulations of two phase liquid gas compositional Darcy flows with phase transitions  

E-print Network

, and the third is an extension to general compositional two phase flows of the pressure pressure formulation, Sg, and the molar fractions of the components c = (c i )iC in each phase Q where Q is the set the component molar fractions c are expressed as functions of the component fugacities f and of the phase

Paris-Sud XI, Université de

377

Influence of guest molecule properties and gas phase composition on hydrate stability  

NASA Astrophysics Data System (ADS)

The stability of a certain gas hydrate phase is usually provided by mechanical, thermal and chemical equilibrium with the coexisting phases: Only if all three conditions of equilibrium are reached the hydrate phase remains stable. Thermal and mechanical equilibrium conditions strongly depend on the composition of the coexisting phases such as vapour phase (feed gas) and liquid phase: 1.) Assuring a chemical equilibrium state between all phases, the stability of the hydrate phase can be estimated from the ratio of the host cavity size compared to the size of the included guest molecule, the guest-to-cavity-ratio. As the enclathrated guest molecules prevent the water cavities from collapsing, a small guest molecule encased into a large hydrate cage may be less stabilizing compared to a well suited guest molecule hindering the water molecules to interact in the way of building new hydrogen bonds. On the other hand, a guest molecule which is as large as the cavity may induce distortions of the cavity structure which also may have destabilizing effects. This hypothesis will be verified by results from systematic experiments concerning the interaction of the guest molecule with the host lattice and the stability limits of the corresponding gas hydrate. 2.) In case of changes of the chemical potential of the coexisting phases, the reestablishment of the chemical equilibrium state is the driving force of all subsequent processes. Even if pressure and temperature conditions are in the stability field of a certain hydrate phase, dissolution, structural transitions and swapping processes regarding the enclathrated guest molecules can be observed. This will be demonstrated with results from experiments on exchange reactions of simple and mixed gas hydrates with CO2.The experiments include microscopic observation, in situ Raman spectroscopy, in situ X-ray diffraction and differential scanning calorimetry. With a better understanding of equilibrium conditions and the guest-host interactions on a molecular level, the impact of destabilizing factors on hydrates in nature will be more predictable.

Schicks, Judith Maria; Luzi, Manja; Strauch, Bettina; Girod, Matthias; Erzinger, Joerg

2010-05-01

378

Incorporating the molecular gas phase in galaxy-size numerical simulations: first applications in dwarf galaxies  

E-print Network

We present models of the evolution of the gaseous and stellar content of galaxies incorporating the formation of H_2 out of HI gas as part of such a model. We do so by formulating a subgrid model for gas clouds that uses well-known cloud scaling relations and solves for the HI-H_2 balance set by the H_2 formation on dust grains and its FUV-induced photodissociation by the temporally and spatially varying interstellar radiation field. This allows the seamless tracking of the evolution of the H_2 gas phase, its precursor Cold Neutral Medium (CNM) HI gas, simultaneously with the star formation. Our most important findings are: a) a significant dependence of the HI-H_2 transition and the resultant H_2 gas mass on the ambient metallicity and the H_2 formation rate, b) the important influence of the characteristic star formation timescale (regulating the ambient FUV radiation field) on the equilibrium H_2 gas mass and c) the possibility of a diffuse H_2 gas phase. Finally, we implement and briefly explore a novel approach of using the ambient H_2 gas mass fraction as a criterion for the onset of star formation. (abridged)

F. I. Pelupessy; P. P. Papadopoulos; P. P. van der Werf

2006-03-21

379

Factors controlling the ice nucleating abilities of ?-pinene SOA particles  

NASA Astrophysics Data System (ADS)

The ice nucleation abilities of fresh, water-soluble, internally mixed, and photochemically oxidized ?-pinene secondary organic aerosol (SOA) particles were investigated at cirrus cloud temperatures in a continuous flow diffusion chamber. SOA sampled from a flow tube (SOA-fresh-FT) mimicked freshly generated particles, while the water-soluble organic compound fraction from a FT and smog chamber (SOA-WSOC-FT, SOA-WSOC-SC) mimicked cloud-processed particles. SOA-fresh-FT, SOA-WSOC-FT, and SOA-WSOC-SC particles were not highly active at nucleating ice between 233 K and 213 K, with activation onsets (i.e., 0.1% of particles forming ice) at or slightly above the theoretical homogeneous freezing line. A significant increase in the O/C of SOA-WSOC-SC via aqueous phase OH oxidation did not modify the ice nucleation abilities, indicating that the detailed composition of the particles is not of paramount importance to their ice nucleating abilities. Instead, precooling the SOA-WSOC-FT and SOA-WSOC-SC particles to 233 K dropped their ice nucleation onsets by up to 20% relative humidity with respect to ice, with lower temperatures likely driving the particles to be more viscous and solid-like. However, it is possible that preactivation contributed to the reduction of the ice nucleation onsets. Particles composed of both SOA-WSOC and ammonium sulfate (AS) were significantly less active in the deposition nucleation mode than pure, solid AS particles.

Ladino, L. A.; Zhou, S.; Yakobi-Hancock, J. D.; Aljawhary, D.; Abbatt, J. P. D.

2014-07-01

380

Grand canonical steady-state simulation of nucleation.  

PubMed

Grand canonical molecular dynamics (GCMD) is applied to the nucleation process in a metastable phase near the spinodal, where nucleation occurs almost instantaneously and is limited to a very short time interval. With a variant of Maxwell's demon, proposed by McDonald [Am. J. Phys. 31, 31 (1963)], all nuclei exceeding a specified size are removed. In such a steady-state simulation, the nucleation process is sampled over an arbitrary time span and all properties of the metastable state, including the nucleation rate, can be obtained with an increased precision. As an example, a series of GCMD simulations with McDonald's demon is carried out for homogeneous vapor to liquid nucleation of the truncated-shifted Lennard-Jones (tsLJ) fluid, covering the entire relevant temperature range. The results are in agreement with direct nonequilibrium MD simulation in the canonical ensemble. It is confirmed for supersaturated vapors of the tsLJ fluid that the classical nucleation theory underpredicts the nucleation rate by two orders of magnitude. PMID:19916595

Horsch, Martin; Vrabec, Jadran

2009-11-14

381

Liquid-gas mixed phase in nuclear matter at finite temperature  

E-print Network

We explore the geometrical structure of Liquid-gas (LG) mixed phase which is relevant to nuclear matter in the crust region of compact stars or supernovae. To get the equation of state (EOS) of the system, the Maxwell construction is found to be applicable to symmetric nuclear matter, where protons and neutrons behave simultaneously. For asymmetric nuclear matter, on the other hand, the phase equilibrium can be obtained by fully solving the Gibbs conditions since the components in the L and G phases are completely different. We also discuss the effects of surface and the Coulomb interaction on the mixed phase.

Toshiki Maruyama; Toshitaka Tatsumi

2010-09-07

382

Shallow n(+) junctions in silicon by arsenic gas-phase doping  

NASA Astrophysics Data System (ADS)

Shallow arsenic junctions were formed in short processing times using gas-phase rapid thermal diffusion with arsine or tertiarybutylarsine (TBA). A 60 s gas-phase diffusion at 1100 C using 3.6% arsine in helium at 760 Torr formed 150 nm junctions with a measured sheet resistance of 100 Omega /d'Alembertian . Shallow junctions were also formed with a 12 min diffusion at 900 C using 10% TBA in argon at 10 Torr. These TBA-formed junctions have arsenic concentration at the silicon surface greater than 1 x 10(sup 20) atms/cu cm and a sheet resistance of 244 Omega /d'Alembertian . In addition, TEM cross sections show no process-induced damage at the junction for gas-phase doping.

Ransom, C. M.; Jackson, T. N.; Degelormo, J. F.; Zeller, C.; Kotecki, D. E.; Graimann, C.; Sadana, D. K.; Benedict, J.

1994-05-01

383

Device for two-dimensional gas-phase separation and characterization of ion mixtures  

DOEpatents

The present invention relates to a device for separation and characterization of gas-phase ions. The device incorporates an ion source, a field asymmetric waveform ion mobility spectrometry (FAIMS) analyzer, an ion mobility spectrometry (IMS) drift tube, and an ion detector. In one aspect of the invention, FAIMS operating voltages are electrically floated on top of the IMS drift voltage. In the other aspect, the FAIMS/IMS interface is implemented employing an electrodynamic ion funnel, including in particular an hourglass ion funnel. The present invention improves the efficiency (peak capacity) and sensitivity of gas-phase separations; the online FAIMS/IMS coupling creates a fundamentally novel two-dimensional gas-phase separation technology with high peak capacity, specificity, and exceptional throughput.

Tang, Keqi (Richland, WA); Shvartsburg, Alexandre A. (Richland, WA); Smith, Richard D. (Richland, WA)

2006-12-12

384

Polymerization in the gas phase, in clusters, and on nanoparticle surfaces.  

PubMed

Gas phase and cluster experiments provide unique opportunities to quantitatively study the effects of initiators, solvents, chain transfer agents, and inhibitors on the mechanisms of polymerization. Furthermore, a number of important phenomena, unique structures, and novel properties may exist during gas-phase and cluster polymerization. In this regime, the structure of the growing polymer may change dramatically and the rate coefficient may vary significantly upon the addition of a single molecule of the monomer. These changes would be reflected in the properties of the oligomers deposited from the gas phase. At low pressures, cationic and radical cationic polymerizations may proceed in the gas phase through elimination reactions. In the same systems at high pressure, however, the ionic intermediates may be stabilized, and addition without elimination may occur. In isolated van der Waals clusters of monomer molecules, sequential polymerization with several condensation steps can occur on a time scale of a few microseconds following the ionization of the gas-phase cluster. The cluster reactions, which bridge gas-phase and condensed-phase chemistry, allow examination of the effects of controlled states of aggregation. This Account describes several examples of gas-phase and cluster polymerization studies where the most significant results can be summarized as follows: (1) The carbocation polymerization of isobutene shows slower rates with increasing polymerization steps resulting from entropy barriers, which could explain the need for low temperatures for the efficient propagation of high molecular weight polymers. (2) Radical cation polymerization of propene can be initiated by partial charge transfer from an ionized aromatic molecule such as benzene coupled with covalent condensation of the associated propene molecules. This novel mechanism leads exclusively to the formation of propene oligomer ions and avoids other competitive products. (3) Structural information on the oligomers formed by gas-phase polymerization can be obtained using the mass-selected ion mobility technique where the measured collision cross-sections of the selected oligomer ions and collision-induced dissociation can provide fairly accurate structural identifications. The identification of the structures of the dimers and trimers formed in the gas-phase thermal polymerization of styrene confirms that the polymerization proceeds according to the Mayo mechanism. Similarly, the ion mobility technique has been utilized to confirm the formation of benzene cations by intracluster polymerization following the ionization of acetylene clusters. Finally, it has been shown that polymerization of styrene vapor on the surface of activated nanoparticles can lead to the incorporation of a variety of metal and metal oxide nanoparticles within polystyrene films. The ability to probe the reactivity and structure of the small growing oligomers in the gas phase can provide fundamental insight into mechanisms of polymerization that are difficult to obtain from condensed-phase studies. These experiments are also important for understanding the growth mechanisms of complex organics in flames, combustion processes, interstellar clouds, and solar nebula where gas-phase reactions, cluster polymerization, and surface catalysis on dust nanoparticles represent the major synthetic pathways. This research can lead to the discovery of novel initiation mechanisms and reaction pathways with applications in the synthesis of oligomers and nanocomposites with unique and improved properties. PMID:18557636

El-Shall, M Samy

2008-07-01

385

Measurements of liquid-phase turbulence in gas-liquid two-phase flows using particle image velocimetry  

NASA Astrophysics Data System (ADS)

Liquid-phase turbulence measurements were performed in an air-water two-phase flow loop with a circular test section of 50 mm inner diameter using a particle image velocimetry (PIV) system. An optical phase separation method--planar laser-induced fluorescence (PLIF) technique—which uses fluorescent particles and an optical filtration technique, was employed to separate the signals of the fluorescent seeding particles from those due to bubbles and other noises. An image pre-processing scheme was applied to the raw PIV images to remove the noise residuals that are not removed by the PLIF technique. In addition, four-sensor conductivity probes were adopted to measure the radial distribution of the void fraction. Two benchmark tests were performed: the first was a comparison of the PIV measurement results with those of similar flow conditions using thermal anemometry from previous studies; the second quantitatively compared the superficial liquid velocities calculated from the local liquid velocity and void fraction measurements with the global liquid flow rate measurements. The differences of the superficial liquid velocity obtained from the two measurements were bounded within ±7% for single-phase flows and two-phase bubbly flows with the area-average void fraction up to 18%. Furthermore, a preliminary uncertainty analysis was conducted to investigate the accuracy of the two-phase PIV measurements. The systematic uncertainties due to the circular pipe curvature effects, bubble surface reflection effects and other potential uncertainty sources of the PIV measurements were discussed. The purpose of this work is to facilitate the development of a measurement technique (PIV-PLIF) combined with image pre-processing for the liquid-phase turbulence in gas-liquid two-phase flows of relatively high void fractions. The high-resolution data set can be used to more thoroughly understand two-phase flow behavior, develop liquid-phase turbulence models, and assess high-fidelity codes for multi-phase flows.

Zhou, Xinquan; Doup, Benjamin; Sun, Xiaodong

2013-12-01

386

Dynamic simulation of dispersed gas-liquid two-phase flow using a discrete bubble model  

Microsoft Academic Search

In this paper a detailed hydrodynamic model for gas-liquid two-phase flow will be presented. The model is based on a mixed Eulerian-Lagrangian approach and describes the time-dependent two-dimensional motion of small, spherical gas bubbles in a bubble column operating in the homogeneous regime. The motion of these bubbles is calculated from a force balance for each individual bubble, accounting for

E. Delnoij; F. A. Lammers; J. A. M. Kuipers; W. P. M. van Swaaij

1997-01-01

387

Effect of Inlet Geometry on Adiabatic Gas-Liquid Two-Phase Flow in a Microchannel  

Microsoft Academic Search

An optical measurement system and video camera were used to investigate gas-liquid two-phase flow characteristics in a circular microchannel of 100 ?m diameter. By cross-correlating the signals from two pairs of optical fibers and infrared photodiodes, void fraction and the lengths and velocities of gas slugs and liquid slugs were measured. The data were obtained using a T-junction with the

Hideo Ide; Ryuji Kimura; Masahiro Kawaji

2008-01-01

388

Challenges in Modeling Gas-Phase Flow in Microchannels: From Slip to Transition  

Microsoft Academic Search

It has long been recognized that the fluid mechanics of gas-phase microflows can differ significantly from the macroscopic world. Non-equilibrium effects such as rarefaction and gas-surface interactions need to be taken into account, and it is well known that the no-slip boundary condition of the Navier-Stokes equations is no longer valid. Following ideas proposed by Maxwell, it is generally accepted

Robert W. Barber; David R. Emerson

2006-01-01

389

Handling two-phase gas condensate flow in offshore pipeline systems  

Microsoft Academic Search

Special flow problems occur in offshore pipelines transmitting gas to processing plants onshore: as the hot, freshly produced gas cools en route, the pipeline pressure falls and the heavier hydrocarbons condense. To aid drilling operators in designing condensate-separation and transport facilities, the following should be considered: (1) temperature behavior and two-phase flow in offshore lines, (2) condensate handling and slug-catcher

Oranje

1983-01-01

390

Handling two-phase gas condensate flow in offshore pipeline systems  

SciTech Connect

Special flow problems occur in offshore pipelines transmitting gas to processing plants onshore: as the hot, freshly produced gas cools en route, the pipeline pressure falls and the heavier hydrocarbons condense. To aid drilling operators in designing condensate-separation and transport facilities, the following should be considered: (1) temperature behavior and two-phase flow in offshore lines, (2) condensate handling and slug-catcher design on booster platforms, (3) onshore separation terminal operation, and (4) the testing of industrial liquid separators.

Oranje, L.

1983-04-18

391

Chiral domains of the SmCPA phase formed by cooling the isotropic liquid or by field-induced nucleation above the clearing temperature  

Microsoft Academic Search

Three homologues belonging to a new class of achiral and asymmetric bent-core mesogens have been synthesized. The mesophase behaviour was investigated using polarizing optical microscopy, and by X-ray and electro-optical measurements. On cooling the isotropic liquid, the SmCPA phase of the dodecyloxy homologue forms a non-birefringent texture which exhibits randomly distributed domains of opposite handedness. Surprisingly, such chiral domains could

Martin W. Schröder; Ulrike Dunemann; Wolfgang Weissflog

2004-01-01

392

Amphipols outperform dodecylmaltoside micelles in stabilizing membrane protein structure in the gas phase.  

PubMed

Noncovalent mass spectrometry (MS) is emerging as an invaluable technique to probe the structure, interactions, and dynamics of membrane proteins (MPs). However, maintaining native-like MP conformations in the gas phase using detergent solubilized proteins is often challenging and may limit structural analysis. Amphipols, such as the well characterized A8-35, are alternative reagents able to maintain the solubility of MPs in detergent-free solution. In this work, the ability of A8-35 to retain the structural integrity of MPs for interrogation by electrospray ionization-ion mobility spectrometry-mass spectrometry (ESI-IMS-MS) is compared systematically with the commonly used detergent dodecylmaltoside. MPs from the two major structural classes were selected for analysis, including two ?-barrel outer MPs, PagP and OmpT (20.2 and 33.5 kDa, respectively), and two ?-helical proteins, Mhp1 and GalP (54.6 and 51.7 kDa, respectively). Evaluation of the rotationally averaged collision cross sections of the observed ions revealed that the native structures of detergent solubilized MPs were not always retained in the gas phase, with both collapsed and unfolded species being detected. In contrast, ESI-IMS-MS analysis of the amphipol solubilized MPs studied resulted in charge state distributions consistent with less gas phase induced unfolding, and the presence of lowly charged ions which exhibit collision cross sections comparable with those calculated from high resolution structural data. The data demonstrate that A8-35 can be more effective than dodecylmaltoside at maintaining native MP structure and interactions in the gas phase, permitting noncovalent ESI-IMS-MS analysis of MPs from the two major structural classes, while gas phase dissociation from dodecylmaltoside micelles leads to significant gas phase unfolding, especially for the ?-helical MPs studied. PMID:25495802

Calabrese, Antonio N; Watkinson, Thomas G; Henderson, Peter J F; Radford, Sheena E; Ashcroft, Alison E

2015-01-20

393

On Capillary Rise and Nucleation  

ERIC Educational Resources Information Center

A comparison of capillary rise and nucleation is presented. It is shown that both phenomena result from a balance between two competing energy factors: a volume energy and a surface energy. Such a comparison may help to introduce nucleation with a topic familiar to the students, capillary rise. (Contains 1 table and 3 figures.)

Prasad, R.

2008-01-01

394

Nucleation and growth of tin whiskers  

NASA Astrophysics Data System (ADS)

Pure tin film of one micron thick was evaporated onto a silicon substrate with chromium and nickel underlayers. The tinned silicon disk was bent by applying a dead load at the center and supported below around the edge to apply biaxial compressive stresses to the tin layer. After 180 C vacuum annealing for 1,2,4,6, and 8 weeks, tin whiskers/hillocks grew. A quantitative method revealed that the overall growth rate decreased with time with a tendency for saturation. A review of the literature showed in general, tin whisker growth has a nucleation period, a growth period and a period of saturation, very similar to recrystallization or phase transformation. In fact we found our data fit Avrami equation very well. This equation shows that the nucleation period was the first week.

Cheng, Jing; Vianco, Paul T.; Zhang, Bei; Li, James C. M.

2011-06-01

395

Plasma-produced phase-pure cuprous oxide nanowires for methane gas sensing  

SciTech Connect

Phase-selective synthesis of copper oxide nanowires is warranted by several applications, yet it remains challenging because of the narrow windows of the suitable temperature and precursor gas composition in thermal processes. Here, we report on the room-temperature synthesis of small-diameter, large-area, uniform, and phase-pure Cu{sub 2}O nanowires by exposing copper films to a custom-designed low-pressure, thermally non-equilibrium, high-density (typically, the electron number density is in the range of 10{sup 11}–10{sup 13}?cm{sup ?3}) inductively coupled plasmas. The mechanism of the plasma-enabled phase selectivity is proposed. The gas sensors based on the synthesized Cu{sub 2}O nanowires feature fast response and recovery for the low-temperature (?140?°C) detection of methane gas in comparison with polycrystalline Cu{sub 2}O thin film-based gas sensors. Specifically, at a methane concentration of 4%, the response and the recovery times of the Cu{sub 2}O nanowire-based gas sensors are 125 and 147?s, respectively. The Cu{sub 2}O nanowire-based gas sensors have a potential for applications in the environmental monitoring, chemical industry, mining industry, and several other emerging areas.

Cheng, Qijin, E-mail: ijin.cheng@xmu.edu.cn; Zhang, Fengyan [School of Energy Research, Xiamen University, Xiamen City, Fujian Province 361005 (China); Yan, Wei [School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney, New South Wales 2052 (Australia); Plasma Nanoscience Laboratories, CSIRO Materials Science and Engineering, Lindfield, New South Wales 2070 (Australia); Randeniya, Lakshman [Plasma Nanoscience Laboratories, CSIRO Materials Science and Engineering, Lindfield, New South Wales 2070 (Australia); Ostrikov, Kostya [Plasma Nanoscience Laboratories, CSIRO Materials Science and Engineering, Lindfield, New South Wales 2070 (Australia); Plasma Nanoscience, School of Physics, The University of Sydney, Sydney, New South Wales 2006 (Australia)

2014-03-28

396

Low liquid loading gas-liquid two-phase flow in near- horizontal pipes  

NASA Astrophysics Data System (ADS)

Low liquid loading gas-liquid two-phase flow in near- horizontal pipes has been studied both experimentally and theoretically. A new state-of-the-art, air-oil test facility was designed, constructed and operated. A transparent test section (50.1-cm ID x 19-m long) could be inclined within +/-2° from the horizontal. Mineral oil was used as the liquid phase (?L = 5.66 mPa.s, ?L = 877 kg/m3, and ? = 30 dynes/cm at 23.9°C) and air was used as the gas phase. The measured parameters included gas flow rate, liquid flow rate, pressure, differential pressure, temperature, liquid holdup, liquid film flow rate, droplet entrainment fraction, droplet deposition rate and liquid film thickness at the bottom of the pipe. A surprising phenomenon was observed; at high gas velocities (annular flow), liquid film flow rate, liquid holdup and pressure gradient decreased as liquid velocity increased. The reason is believed to be the effect of droplet entrainment on the gas stream. Countercurrent flow and vortices in the liquid film were observed in upward inclined flows. Gas bubbles were observed in the liquid film at all five inclination angles. A two-fluid model was developed for low liquid loading flows. New correlations were proposed for the interfacial friction factor. The effect of droplet entrainment on the interfacial friction factor is also evaluated. The predictions of liquid holdup and pressure gradient from the new models matched well with the experimental data.

Meng, Weihong

397

Atmospheric chemistry of gas-phase polycyclic aromatic hydrocarbons: formation of atmospheric mutagens.  

PubMed Central

The atmospheric chemistry of the 2- to 4-ring polycyclic aromatic hydrocarbons (PAH), which exist mainly in the gas phase in the atmosphere, is discussed. The dominant loss process for the gas-phase PAH is by reaction with the hydroxyl radical, resulting in calculated lifetimes in the atmosphere of generally less than one day. The hydroxyl (OH) radical-initiated reactions and nitrate (NO3) radical-initiated reactions often lead to the formation of mutagenic nitro-PAH and other nitropolycyclic aromatic compounds, including nitrodibenzopyranones. These atmospheric reactions have a significant effect on ambient mutagenic activity, indicating that health risk assessments of combustion emissions should include atmospheric transformation products. PMID:7821285

Atkinson, R; Arey, J

1994-01-01

398

Gas Phase Spectra and Structural Determination of Glucose 6 Phosphate Using Cryogenic Ion Vibrational Spectroscopy  

NASA Astrophysics Data System (ADS)

Glucose-6-Phosphate (G6P) is one member of a class of simple phosphorylated sugars that are relevant in biological processes. We have acquired a gas phase infrared spectrum of G6P- using cryogenic ion vibrational spectroscopy (CIVS) in a home-built spectrometer. The experimental spectrum was compared with calculated vibrational spectra from a systematic conformer search. For both of the ? and ? anomers, results show that only the lowest energy conformers are present in the gas phase. If spectral signatures for similar sugars could be cataloged, it would allow for conformer-specific determination of mixture composition, for example, for glycolyzation processes.

Kregel, Steven J.; Voss, Jonathan; Marsh, Brett; Garand, Etienne

2014-06-01

399

Gas-phase formation of silicon carbides, oxides, and sulphides from atomic silicon ions  

NASA Technical Reports Server (NTRS)

A systematic experimental study of the kinetics and mechanisms of the chemical reactions in the gas phase between ground-state Si(+)2p and a variety of astrophysical molecules. The aim of this study is to identify the reactions which trigger the formation of chemical bonds between silicon and carbon, oxygen and sulphur, and the chemical pathways which lead to further molecular growth. Such knowledge is valuable in the identification of new extraterrestrial silicon-bearing molecules and for an assessment of the gas-phase transition from atomic silicon to silicon carbide and silicate grain particles in carbon-rich and oxygen-rich astrophysical environments.

Bohme, Diethard K.; Wlodek, Stanislaw; Fox, Arnold

1989-01-01

400

Determination of doubly labeled water by gas-phase Fourier transform infrared spectroscopy.  

PubMed

Both 2H (deuterium) and 18O (oxygen 18) in isotopically enriched water have been detected by gas-phase Fourier transform infrared (FTIR) spectroscopy at 2,720 and 3,661.8 cm-1, respectively. A linear relationship between varying concentrations of each of these isotopes and their absorbance at the above frequencies indicates that gas-phase FTIR may provide a rapid and potentially less expensive approach to measure doubly labeled water in biological fluids for the estimation of energy expenditure and total body water. PMID:7854152

Khaled, M A; Krumdieck, C L; Ong, J L

1995-01-01

401

Direct gas-phase epoxidation of propylene to propylene oxide through radical reactions: A theoretical study  

NASA Astrophysics Data System (ADS)

The gas-phase radical chain reactions which utilize O 2 as the oxidant to produce propylene oxide (PO) are investigated through theoretical calculations. The transition states and energy profiles were obtained for each path. The rate constants were also calculated. The energetics for the competing pathways indicate that PO can be formed selectively due to its relatively low activation barrier (9.3 kcal/mol) which is in a good agreement with the experimental value (11 kcal/mol) of gas-phase propylene epoxidation. The formation of the acrolein and combustion products have relatively high activation barriers and are not favored. These results also support the recent experimental findings.

Kizilkaya, Ali Can; Fellah, Mehmet Ferdi; Onal, Isik

2010-03-01

402

Liquid-gas Phase Transition in Strange Hadronic Matter with Weak Y-Y Interaction  

E-print Network

The liquid-gas phase transition in strange hadronic matter is reexamined by using the new parameters about the $\\Lambda - \\Lambda$ interaction deduced from recent observation of $^{6}_{\\Lambda\\Lambda}He$ double hypernucleus. The extended Furnstahl-Serot-Tang model with nucleons and hyperons is utilized. The binodal surface, the limit pressure, the entropy, the specific heat capacity and the Caloric curves are addressed. We find that the liquid-gas phase transition can occur more easily in strange hadronic matter with weak Y-Y interaction than that of the strong Y-Y interaction.

Li Yang; Shao Yu Yin; Wei Liang Qian; Ru-keng Su

2005-06-19

403

Study of Hind Limb Tissue Gas Phase Formation in Response to Suspended Adynamia and Hypokinesia  

NASA Technical Reports Server (NTRS)

The purpose of this study was to investigate the hypothesis that reduced joint/muscle activity (hypo kinesia) as well as reduced or null loading of limbs (adynamia) in gravity would result in reduced decompression-induced gas phase and symptoms of decompression sickness (DCS). Finding a correlation between the two phenomena would correspond to the proposed reduction in tissue gas phase formation in astronauts undergoing decompression during extravehicular activity (EVA) in microgravity. The observation may further explain the reported low incidence of DCS in space.

Butler, Bruce D.

1996-01-01

404

An approximate calculation of advective gas-phase transport of 14C at Yucca Mountain, Nevada  

NASA Astrophysics Data System (ADS)

A quasilinear partial differential equation, which describes gas-phase transport of a 14C kinematic wave through a porous medium, is derived, its sensitivity to system variables is analyzed and it is applied to one possible release scenarion at the porposed Yucca Mountain, Nevada high-level radioactive waste repository. Advection, isotope exchange between CO 2 in a flowing gas phase and HCO 3- in a static aqueous phase, and radioactive decay are incorporated. The governing equation is solved analytically by the method of characteristics. The mass fraction of 14C in the gas phase,X 14g, is controlled by radioactive decay. The relatively long half-line of 14C, about 5720 years, and the relatively shallow proposed burial depth of the radioactive waste, about 350m, requires significant retardation of the 14C wave velocity for significant reduction in X 14g. 14C wave velocity is most sensitive to temperature and pH which control the distribution of total carbon between gas and liquid phase; the greater the partitioning of carbon into the liquid phase, the greater the retardation of the 14C wave velocity and the greater the ultimate reduction in X 14g from initial conditions. Partitioning of total carbon into the liquid phase is greatest at low temperatures, < 100° C, and high pH values, > 8. Increasing water saturation also tends to retard 14C wave velocity but to a lesser extent. The governing equation has been applied using conditions that may possibly occur at the proposed Yucca Mountain repository. Calculations indicate that the 14C wave takes about 5900 years to reach the surface with a X 14g equal to 25 ppm. Diffusion and dispersion are not of major importance for these conditions. These calculations are approximate due to the number of assumptions involved. Discharge of 14C into the gas before the selected time would accelerate wave arrival and increase the amount of 14C reaching the surface.

Knapp, R. B.

1990-01-01

405

Selective removal of ethylene, a deposit precursor, from a "dirty" synthesis gas stream via gas-phase partial oxidation.  

PubMed

A fundamental issue in the gasification of biomass is that in addition to the desired synthesis gas product (a mixture of H(2) and CO), the gasifier effluent contains other undesirable products that need to be removed before any further downstream processing can occur. This work assesses the potential to selectively remove hydrocarbons from a synthesis gas stream via gas-phase partial oxidation. Specifically, the partial oxidation of methane-doped, ethylene-doped, and methane/ethylene-doped model synthesis gas mixtures has been investigated at ambient pressures over a temperature range of 760-910 degrees C and at residence times ranging from 0.4 to 2.4 s using a tubular flow reactor. For the synthesis gas mixtures that contain either methane or ethylene, the addition of oxygen substantially reduces the hydrocarbon concentration while only a small reduction in the hydrogen concentration is observed. For the synthesis gas mixtures doped with both methane and ethylene, the addition of oxygen preferentially removes ethylene while the concentrations of methane and hydrogen remain relatively unaffected. These results are compared to the predictions of a plug flow model using a reaction mechanism that is designed to describe the pyrolysis and partial oxidation of small hydrocarbon species. The agreement between the experimental observations and the model predictions is quite good, allowing us to explore the underlying chemistry that leads to the hydrocarbon selective oxidation. The implications of these results are briefly discussed in terms of using synthesis gas to produce liquid fuels and electrical power via a solid oxide fuel cell. PMID:20496944

Villano, Stephanie M; Hoffmann, Jessica; Carstensen, Hans-Heinrich; Dean, Anthony M

2010-06-17

406

Gas-liquid mass transfer in a three-phase fluidized bed containing low density particles  

SciTech Connect

Gas-liquid mass-transfer behavior in a three-phase fluidized bed containing particles with properties comparable to those of bioparticles used in biological processes was examined. The volumetric gas-liquid mass-transfer coefficients, k{sub L}a, decrease with increasing solid concentration and with increasing terminal velocity of particles. An increase in the liquid velocity significantly increases k{sub L}a, but only slightly increases the gas holdup, thus suggesting a significant liquid velocity effect on k{sub L}.

Tang, W.T. (Shell Development Co., Houston, TX (USA)); Fan, L.S. (Ohio State Univ., Columbus, OH (USA). Dept. of Chemical Engineering)

1990-01-01

407

In situ gas-phase hydrosilylation of plasma-synthesized silicon nanocrystals.  

PubMed

Surface passivation of semiconductor nanocrystals (NCs) is critical in enabling their utilization in novel optoelectronic devices, solar cells, and biological and chemical sensors. Compared to the extensively used liquid-phase NC synthesis and passivation techniques, gas-phase routes provide the unique opportunity for in situ passivation of semiconductor NCs. Herein, we present a method for in situ gas-phase organic functionalization of plasma-synthesized, H-terminated silicon (Si) NCs. Using real-time in situ attenuated total reflection Fourier transform IR spectroscopy, we have studied the surface reactions during hydrosilylation of Si NCs at 160 °C. First, we show that, during gas-phase hydrosilylation of Si NCs using styrene (1-alkene) and acetylene (alkyne), the reaction pathways of the alkenes and alkynes chemisorbing onto surface SiH(x) (x = 1-3) species are different. Second, utilizing this difference in reactivity, we demonstrate a novel pathway to enhance the surface ligand passivation of Si NCs via in situ gas-phase hydrosilylation using the combination of a short-chain alkyne (acetylene) and a long-chain 1-alkene (styrene). The quality of surface passivation is further validated through IR and photoluminescence measurements of Si NCs exposed to air. PMID:21774486

Jariwala, Bhavin N; Dewey, Oliver S; Stradins, Paul; Ciobanu, Cristian V; Agarwal, Sumit

2011-08-01

408

Shape and area fluctuation effects on nucleation theory  

NASA Astrophysics Data System (ADS)

In standard nucleation theory, the nucleation process is characterized by computing ??(V), the reversible work required to form a cluster of volume V of the stable phase inside the metastable mother phase. However, other quantities besides the volume could play a role in the free energy of cluster formation, and this will in turn affect the nucleation barrier and the shape of the nucleus. Here we exploit our recently introduced mesoscopic theory of nucleation to compute the free energy cost of a nearly spherical cluster of volume V and a fluctuating surface area A, whereby the maximum of ??(V) is replaced by a saddle point in ??(V, A). Compared to the simpler theory based on volume only, the barrier height of ??(V, A) at the transition state is systematically larger by a few kBT. More importantly, we show that, depending on the physical situation, the most probable shape of the nucleus may be highly non-spherical, even when the surface tension and stiffness of the model are isotropic. Interestingly, these shape fluctuations do not influence or modify the standard Classical Nucleation Theory manner of extracting the interface tension from the logarithm of the nucleation rate near coexistence.

Prestipino, Santi; Laio, Alessandro; Tosatti, Erio

2014-03-01

409

Surface nanobubbles nucleate microdroplets.  

PubMed

When a hydrophobic solid is in contact with water, surface nanobubbles often form at the interface. They have a lifetime many orders of magnitude longer than expected. Here, we show that they even withstand a temperature increase to temperatures close to the boiling point of bulk water; i.e., they do not nucleate larger bubbles ("superstability"). On the contrary, when the vapor-liquid contact line passes a nanobubble, a liquid film remains around it, which, after pinch-off, results in a microdroplet in which the nanobubbles continue to exist. Finally, the microdroplet evaporates and the nanobubble consequently bursts. Our results support that pinning plays a crucial role for nanobubble stability. PMID:24765973

Zhang, Xuehua; Lhuissier, Henri; Sun, Chao; Lohse, Detlef

2014-04-11

410

A three-phase free boundary problem with melting ice and dissolving gas  

E-print Network

We develop a mathematical model for a three-phase free boundary problem in one dimension that involves the interactions between gas, water and ice. The dynamics are driven by melting of the ice layer, while the pressurized gas also dissolves within the meltwater. The model incorporates a Stefan condition at the water-ice interface along with Henry's law for dissolution of gas at the gas-water interface. We employ a quasi-steady approximation for the phase temperatures and then derive a series solution for the interface positions. A non-standard feature of the model is an integral free boundary condition that arises from mass conservation owing to changes in gas density at the gas-water interface, which makes the problem non-self-adjoint. We derive a two-scale asymptotic series solution for the dissolved gas concentration, which because of the non-self-adjointness gives rise to a Fourier series expansion in eigenfunctions that do not satisfy the usual orthogonality conditions. Numerical simulations of the original governing equations are used to validate the series approximations.

Maurizio Ceseri; John M. Stockie

2014-11-05

411

Microporous hydrophobic hollow fiber modules for gas-liquid phase separation in microgravity  

NASA Astrophysics Data System (ADS)

Gas-liquid interphase mass transfer operations, such as gas-liquid phase separation, gas absorption into liquid or dissolved gas separation from liquid, gas humidification and drying via liquid contact, and evaporative cooling are readily accomplished on the Earth with settling/spray chambers, packed towers, or bubble columns. This paper reports on gas-water mass transfer tests performed utilizing microporous hydrophobic Hollow Fiber Modules (HFMs) of the type currently employed as blood oxygenators in heart-lung machines. In these HFMs, gases are transferrred to and from water or other hydrophilic liquids through the microporous fiber walls; liquid water does not enter the pores of the highly hydrophobic wall material. The experiments included air-water phase separation, absorption of oxygen and carbon dioxide into water and separation of these dissolved gases from water, air humidification and drying by contact with temperature-controlled water, and controlled evaporation of water into a vacuum. In each of these experiments, a small, light HFM sucessfully performed the mass tranfer function, with no leakage of liquid water through the porous walls of the hollow fibers, even with high pressure across the fiber wall for extended periods of time. These results demonstrate that gas-liquid mass transfer unit operations on hydrophilic liquids, implemented with microporous hydrophobic HFM technology, are ready for use in microgravity fluid processing systems.

Noyes, Gary

412

Comparison of the relative importance of helium and vacancy accumulation in void nucleation  

SciTech Connect

Void nucleation in irradiated austenitic stainless steels generally requires the presence of either residual or transmutant gases. Classical nucleation rates are much too low to account for the number of voids observed at temperatures greater than about 450/sup 0/C. An alternate path is generally believed to be responsible for void formation; viz. the growth of gas-stabilized bubbles until they reach a critical size beyond which further gas accumulation is not required to promote growth. Two limiting paths can be envisioned for void nucleation on a population of sub-critical helium/vacancy clusters; one is limited to growth by helium accumulation along and the other to growth by stochastic fluctuations in the vacancy accumulation. As bubbles approach the critical size, stochastic processes could begin to contribute to the void nucleation rate. A comparison is made of nucleation rates along these two limiting paths as a function of the gas content of the clusters.

Stoller, R.E.; Odette, G.R.

1986-06-01

413

Photostability of gas- and solid-phase biomolecules under astrophysical analog soft X-rays field  

NASA Astrophysics Data System (ADS)

We present experimental studies on the interaction of soft X-rays on gas-phase and solid-phase amino acids and nucleobases in an attempt to verify if these molecules (supposed to be formed in molecular clouds/protostellar clouds) can survive long enough to be observed or even to be found in meteorites. Measurements have been undertaken employing 150 eV photons under high vacuum conditions at the Brazilian Synchrotron Light Laboratory (LNLS). The produced ions from the gas-phase experiments (glycine, adenine and uracil) have been mass/charge analyzed by time-of-flight spectrometer. The analysis of solid phase samples (glycine, DL-proline, DL-valine, adenine and uracil) were performed by a Fourier transform infrared spectrometer coupled to the experimental chamber. Photodissociation cross sections and halflives were determined and extrapolated to astrophysical environments. The nucleobases photostability was up to two orders of magnitude higher than for the amino acids.

Pilling, S.; Andrade, D. P. P.; Marinho, R. T.; do Nascimento, E. M.; Boechat-Roberty, H. M.; de Castilho, R. B.; de Souza, G. G. B.; Coutinho, L. H.; Cavasso-Filho, R. L.; Lago, A. F.; de Brito, A. N.

2010-03-01

414

Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow  

SciTech Connect

Gas-water two phase flow phenomenon widely exists in production and living and the measurement of it is meaningful. A new type of long-waist cone flow sensor has been designed to measure two-phase mass flow rate. Six rings structure of conductance probe is used to measure volume fraction and axial velocity. The calibration of them have been made. Two sensors have been combined in horizontal pipeline experiment to measure two-phase flow mass flow rate. Several model of gas-water two-phase flow has been discussed. The calculation errors of total mass flow rate measurement is less than 5% based on the revised homogeneous flow model.

Wu, Hao; Dong, Feng [Tianjin Key Laboratory of Process Measurement and Control, School of Electrical Engineering and Automation, Tianjin University, Tianjin (China)

2014-04-11

415

Experimental on two sensors combination used in horizontal pipe gas-water two-phase flow  

NASA Astrophysics Data System (ADS)

Gas-water two phase flow phenomenon widely exists in production and living and the measurement of it is meaningful. A new type of long-waist cone flow sensor has been designed to measure two-phase mass flow rate. Six rings structure of conductance probe is used to measure volume fraction and axial velocity. The calibration of them have been made. Two sensors have been combined in horizontal pipeline experiment to measure two-phase flow mass flow rate. Several model of gas-water two-phase flow has been discussed. The calculation errors of total mass flow rate measurement is less than 5% based on the revised homogeneous flow model.

Wu, Hao; Dong, Feng

2014-04-01

416

The interstellar gas-phase chemistry of HCN and HNC  

NASA Astrophysics Data System (ADS)

We review the reactions involving hydrogen cyanide (HCN) and hydrogen isocyanide (HNC) in dark molecular clouds to elucidate new chemical sources and sinks of these isomers. We find that the most important reactions for the HCN-HNC system are dissociative recombination (DR) reactions of HCNH+ (HCNH+ + e-), the ionic CN + H3+, HCN + C+, HCN and HNC reactions with H+/He+/H3+/H3O+/HCO+, the N + CH2 reaction and two new reactions: H + CCN and C + HNC. We test the effect of the new rate constants and branching ratios on the predictions of gas-grain chemical models for dark cloud conditions. The rapid C + HNC reaction keeps the HCN/HNC ratio significantly above 1 as long as the carbon atom abundance remains high. However, the reaction of HCN with H3+ followed by DR of HCNH+ acts to isomerize HCN into HNC when carbon atoms and CO are depleted leading to an HCN/HNC ratio close to or slightly greater than 1. This agrees well with observations in TMC-1 and L134N taking into consideration the overestimation of HNC abundances through the use of the same rotational excitation rate constants for HNC as for HCN in many radiative transfer models.

Loison, Jean-Christophe; Wakelam, Valentine; Hickson, Kevin M.

2014-09-01

417

Gas phase water in the surface layer of protoplanetary disks  

E-print Network

Recent observations of the ground state transition of HDO at 464 GHz towards the protoplanetary disk of DM Tau have detected the presence of water vapor in the regions just above the outer disk midplane (Ceccarelli et al 2005). In the absence of non-thermal desorption processes, water should be almost entirely frozen onto the grain mantles and HDO undetectable. In this Letter we present a chemical model that explores the possibility that the icy mantles are photo-desorbed by FUV (6eV water vapor above the disk midplane over the entire disk. Assuming a photo-desorption yield of 10^{-3}, the water abundance in this layer is predicted to be ~ 3 x 10^{-7} and the average H2O column density is ~ 1.6x 10^{15} cm^{-2}. The predictions are very weakly dependent on the details of the model, like the incident FUV radiation field, and the gas density in the disk. Based on this model, we predict a gaseous HDO/H2O ratio in DM Tau of ~1%. In addition, we predict the ground state transition of water at 557 GHz to be undetectable with ODIN and/or HSO-HIFI.

C. Dominik; C. Ceccarelli; D. Hollenbach; M. Kaufman

2005-10-21

418

Gas adsorption/absorption heat switch, phase 1  

NASA Technical Reports Server (NTRS)

The service life and/or reliability of far-infrared sensors on surveillance satellites is presently limited by the cryocooler. The life and/or reliability, however, can be extended by using redundant cryocoolers. To reduce parasitic heat leak, each stage of the inactive redundant cryocooler must be thermally isolated from the optical system, while each stage of the active cryocooler must be thermally connected to the system. The thermal break or the thermal contact can be controlled by heat switches. Among different physical mechanisms for heat switching, mechanically activated heat switches tend to have low reliability and, furthermore, require a large contact force. Magnetoresistive heat switches are, except at very low temperatures, of very low efficiency. Heat switches operated by the heat pipe principle usually require a long response time. A sealed gas gap heat switch operated by an adsorption pump has no mechanical motion and should provide the reliability and long lifetime required in long-term space missions. Another potential application of a heat switch is the thermal isolation of the optical plane during decontamination.

Chan, C. K.

1987-01-01

419

In situ measurements of gas/particle-phase transitions for atmospheric semivolatile organic compounds  

PubMed Central

An understanding of the gas/particle-phase partitioning of semivolatile compounds is critical in determining atmospheric aerosol formation processes and growth rates, which in turn affect global climate and human health. The Study of Organic Aerosol at Riverside 2005 campaign was performed to gain a better understanding of the factors responsible for aerosol formation and growth in Riverside, CA, a region with high concentrations of secondary organic aerosol formed through the phase transfer of low-volatility reaction products from the oxidation of precursor gases. We explore the ability of the thermal desorption aerosol gas chromatograph (TAG) to measure gas-to-particle-phase transitioning for several organic compound classes (polar and nonpolar) found in the ambient Riverside atmosphere by using in situ observations of several hundred semivolatile organic compounds. Here we compare TAG measurements to modeled partitioning of select semivolatile organic compounds. Although TAG was not designed to quantify the vapor phase of semivolatile organics, TAG measurements do distinguish when specific compounds are dominantly in the vapor phase, are dominantly in the particle phase, or have both phases present. Because the TAG data are both speciated and time-resolved, this distinction is sufficient to see the transition from vapor to particle phase as a function of carbon number and compound class. Laboratory studies typically measure the phase partitioning of semivolatile organic compounds by using pure compounds or simple mixtures, whereas hourly TAG phase partitioning measurements can be made in the complex mixture of thousands of polar/nonpolar and organic/inorganic compounds found in the atmosphere. PMID:20142511

Williams, Brent J.; Goldstein, Allen H.; Kreisberg, Nathan M.; Hering, Susanne V.

2010-01-01

420

Isospin and momentum dependence of liquid-gas phase transition in hot asymmetric nuclear matter  

E-print Network

The liquid-gas phase transition in hot neutron-rich nuclear matter is investigated within a self-consistent thermal model using different interactions with or without isospin and/or momentum dependence. The boundary of the phase-coexistence region is shown to be sensitive to the density dependence of the nuclear symmetry energy as well as the isospin and momentum dependence of the nuclear interaction.

Jun Xu; Lie-Wen Chen; Bao-An Li; Hong-Ru Ma

2007-11-12

421

A flow pattern map for two-phase liquid-gas flows under reduced gravity conditions  

Microsoft Academic Search

Two-phase gas-liquid flows have a wide range of applications in space including the flow of cryogenics in transport lines and heat-transfer fluids in a thermal control system. The behavior of these systems under reduced gravity must be understood in order to optimize the design and maintenance of such systems. Experimental studies on two-phase flow patterns and their transitions were conducted

K. S Rezkallah; L. Zhao

1995-01-01

422

Determination of Dioxin by Solid Phase Microextraction Coupled with Gas Chromatography\\/Mass Spectrometry  

Microsoft Academic Search

Objective :A sensitive and accurate method has been developed for the determination of Dioxin by solid phase microextraction(SPME)coupled with gas chromatography and mass spectrometric detection(GC-MS). Method: Some factors influencing solid-phase microexaction(SPME) extraction efficiency such as extraction of time and temperature were studied. The result shows: with the extraction of time 30 min, temperature 45degC, Detection limit of the method is

Liu YanQun; TanYou Ming; Zhou Yi Kai

2008-01-01

423

Effect of shear viscosity on the nucleation of antikaon condensed matter in neutron stars  

NASA Astrophysics Data System (ADS)

We investigate a first-order phase transition from hadronic matter to antikaon condensed matter during the cooling stage of protoneutron stars. The phase transition proceeds through the thermal nucleation of antikaon condensed matter. In this connection we study the effect of shear viscosity on the thermal nucleation rate of droplets of antikaon condensed matter. Here we adopt the same equation of state for the calculation of shear viscosity and thermal nucleation time. We compute the shear viscosity of neutron star matter composed of neutrons, protons, electrons, and muons using the relativistic mean field model. The prefactor in the nucleation rate, which includes the shear viscosity, is enhanced by several orders of magnitude compared with the T4 approximation of earlier calculations. Consequently the thermal nucleation time in the T4 approximation overestimates our result. Further, the thermal nucleation of an antikaon droplet might be possible in our case for surface tension smaller than 20MeVfm-2.

Banik, Sarmistha; Bandyopadhyay, Debades

2010-12-01

424

Atmospheric pressure flow reactor / aerosol mass spectrometer studies of tropospheric aerosol nucleat and growth kinetics. Final report, June, 2001  

SciTech Connect

The objective of this program was to determine the mechanisms and rates of growth and transformation and growth processes that control secondary aerosol particles in both the clear and polluted troposphere. The experimental plan coupled an aerosol mass spectrometer (AMS) with a chemical ionization mass spectrometer to provide simultaneous measurement of condensed and particle phases. The first task investigated the kinetics of tropospheric particle growth and transformation by measuring vapor accretion to particles (uptake coefficients, including mass accommodation coefficients and heterogeneous reaction rate coefficients). Other work initiated investigation of aerosol nucleation processes by monitoring the appearance of submicron particles with the AMS as a function of precursor gas concentrations. Three projects were investigated during the program: (1) Ozonolysis of oleic acid aerosols as model of chemical reactivity of secondary organic aerosol; (2) Activation of soot particles by measurement deliquescence in the presence of sulfuric acid and water vapor; (3) Controlled nucleation and growth of sulfuric acid aerosols.

Worsnop, Douglas R.

2001-06-01

425

A microcomputer-controlled gas phase microreactor system  

SciTech Connect

Although automated reactors are effective tools for studying a single type of reaction or optimizing catalyst performance, they may not be well suited for exploratory research. These reactors generally have several shortcomings. First, they may have limited versatility since they are usually designed with a single application in mind. Second, computer systems used for process control and data acquisition are often expensive and complex, so that once they are set up for a given application, it is quite difficult to adapt them for another. Because of these restrictions, experimental reactors are often operated manually, requiring a full-time operator to monitor operations and acquire data. This is a greater problem in laboratories where projects are often short-term, and the costs of setting up an automated reactor may outweigh the benefits of automation. For an automated reactor to be cost-effective in such an environment, both reactor hardware and control software must be versatile enough that they can be easily modified and adapted for different experiments. An automated gas-flow microreactor has been designed and constructed which is both inexpensive and flexible. The reactor is capable of performing three different types of experiments, 1) continuous reagent feed with analysis of the product stream, 2) pulsed-flow experiments, and 3) temperature-programmed desorption (TPD) and reaction (TPR). Conversion of the reactor from one configuration to another requires less than one hour. Process control and data acquisition are performed using an Apple II Plus microcomputer (Apple Computer Corp., Cupertino, Calif.) and an ISAAC interface device (Cyborg Corp., Newton, Mass.).

Morris, R.M.

1983-08-01

426

MOLECULAR SPECTROSCPY AND REACTIONS OF ACTINIDES IN THE GAS PHASE AND CRYOGENIC MATRICES  

SciTech Connect

In this chapter we review the spectroscopic data for actinide molecules and the reaction dynamics for atomic and molecular actinides that have been examined in the gas phase or in inert cryogenic matrices. The motivation for this type of investigation is that physical properties and reactions can be studied in the absence of external perturbations (gas phase) or under minimally perturbing conditions (cryogenic matrices). This information can be compared directly with the results from high-level theoretical models. The interplay between experiment and theory is critically important for advancing our understanding of actinide chemistry. For example, elucidation of the role of the 5f electrons in bonding and reactivity can only be achieved through the application of experimentally verified theoretical models. Theoretical calculations for the actinides are challenging due the large numbers of electrons that must be treated explicitly and the presence of strong relativistic effects. This topic has been reviewed in depth in Chapter 17 of this series. One of the goals of the experimental work described in this chapter has been to provide benchmark data that can be used to evaluate both empirical and ab initio theoretical models. While gas-phase data are the most suitable for comparison with theoretical calculations, there are technical difficulties entailed in generating workable densities of gas-phase actinide molecules that have limited the range of species that have been characterized. Many of the compounds of interest are refractory, and problems associated with the use of high temperature vapors have complicated measurements of spectra, ionization energies, and reactions. One approach that has proved to be especially valuable in overcoming this difficulty has been the use of pulsed laser ablation to generate plumes of vapor from refractory actinide-containing materials. The vapor is entrained in an inert gas, which can be used to cool the actinide species to room temperature or below. For many spectroscopic measurements, low temperatures have been achieved by co-condensing the actinide vapor in rare gas or inert molecule host matrices. Spectra recorded in matrices are usually considered to be minimally perturbed. Trapping the products from gas-phase reactions that occur when trace quantities of reactants are added to the inert host gas has resulted in the discovery of many new actinide species. Selected aspects of the matrix isolation data were discussed in chapter 17. In the present chapter we review the spectroscopic matrix data in terms of its relationship to gas-phase measurements, and update the description of the new reaction products found in matrices to reflect the developments that have occurred during the past two years. Spectra recorded in matrix environments are usually considered to be minimally perturbed, and this expectation is borne out for many closed shell actinide molecules. However, there is growing evidence that significant perturbations can occur for open shell molecules, resulting in geometric distortions and/or electronic state reordering. Studies of actin